Metric units of measurement

The French Academy of Sciences in the late 1700’s set out to make a simple and reliable measurement system. Over the next 200 years, the metric system was formed. This system is now the International System of Units (SI). We will be working with mass, volume, length, and temperature in our metric studies and conversions.

When working with mass, volume, and length, the “metric staircase” is a helpful visual tool, especially when doing conversions between units:

If going from a big to a smaller unit, move decimal point to RIGHT the number of times you jump down the staircase.

Ex.- 1 meter = _______millimeters

Meters to millimeters is 3 jumps. So there’s a decimal point after 1. Move decimal point 3 places to right.

1. _ _ _ = 1000.

So 1 meter = 1000 millimeters

dkm

You can remember how the order of the units goes by remembering a simple mnemonic, or memory aide: King Henry Died Monday Drinking Chocolate Milk.

You can use the metric staircase for meters (length), as we did above, or grams (mass), or liters (volume). Just be sure to substitute the ‘m’ on the right of the unit with ‘L’ for liters and ‘g’ for grams (km – kL – kg).

Common SI (Metric) units:

km (kilometer) = 1000 meters

hm (hectometer) = 100 meters

dkm (dekameter) = 10 meters

m (meter) = 1 meter (base unit)

dm (decimeter) = 1/10 of meter

cm (centimeter) = 1/100 of meter

mm (millimeter) = 1/1000 of meter

The Scientific Method is a useful tool for engaging in scientific inquiry. The traditional steps are:

Observe
Ask a question
Research
Form a hypothesis
Test the hypothesis
Record and analyze data
Form a conclusion

It is also important to repeat your experiment, to exclude the possibility of error in your experimental setup. You also must communicate your results to the rest of the scientific community. In this way, you contribute to building up of knowledge and experience in a particular scientific discipline, and others benefit from your work.

Let’s put these steps into a practical example. You might observe that leaves are starting to change from green to shades of red, brown, and orange during the fall season. You then ask a question: “What is causing the leaves to change color during this time every year?” You then do some background research. You are now in a position to form a hypothesis: The leaves are changing color as a result of chemical reactions occurring. You must test this hypothesis, and then record and analyze data that you obtain. Only now can you form a reasonable conclusion: The leaves are changing color because of a breakdown in chlorophyll, and secondary chemical reactions that cause the green color to disappear and hues of red, brown, and orange to appear in its place.

Experiments are made up of variables, which are factors in an experiment that change. The Independent Variable (IV) is the factor that the experimenter changes on purpose. In an experiment that seeks to determine the effect of differing amounts of water on plant growth, the differing amounts of water would be the IV – the experimenter might give Plant A 10mL of water, Plant B 20mL, Plant C 30mL, and Plant D 40mL. The factor that changes as a result of the purposely-changed factor is called the Dependent Variable (DV). In other words, the experiment changes it. In our plant growth experiment example, plant growth would be the DV. The independent variable will have different levels, or ways that the experimenter changes it – this is referred to as Level of Independent Variable (LIV). In our example, the different ways that he/she changes, or manipulates the IV are applying 10, 20, 30, and 40mL of water to the different plants. Variables that do not change in an experiment are called Constants. In our sample experiment, some constants might be same type of water (distilled), same type of soil, same type of pot, etc.). An experiment will usually have a Control. A control group is used for comparison with the experimental groups. So in our example, Plant E might be the control – it is not given any water. It is a good idea to repeat our experiment, to reduce the possibility of error. So the Number of Repeated Trials (NRT) refers to the number of times that each level of independent variable is tested. In our example, Plants A-D will be given the specified amounts of water (10, 20, 30, and 40mL) of water a total of three times – so the NRT for this experiment would be 3.

u We want to be able to formulate good title and hypothesis statements for our experiment. When you write an experimental title, you are basically stating what the effect of the independent variable is on the dependent variable, and you write it in this format:

The Effect of IV on DV.

So a good title for our plant experiment would be:

The Effect of Amount of Water on Plant Height.

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IV DV

We then can write a hypothesis statement for our experiment. Hypothesis statements follow an “If, then” format. Basically, in a hypothesis statement you are making a prediction about how the dependent variable will change if you make a certain change to the independent variable: If how you are changing the IV, then how you predict the DV will change. So a good hypothesis statement for our experiment would be:

If the amount of water given a plant is increased, then the height the plant will grow will be increased.

There are of course several different hypothesis statements that could be written for an experiment such as this. Some are written in such a way that a change in magnitude in the IV reflects a similar magnitude change in the DV. These are in direct proportion:

If IV increases, then DV increases.

If the amount of water given a plant is increased, then the plant height will be increased.

If IV decreases, then DV decreases.

If the amount of water given a plant is decreased, then the plant height will be decreased.

Others are written in such a way that a change in magnitude in the IV reflects the opposite change in magnitude in the DV. These are in inverse proportion:

If IV increases, then DV decreases.

If the amount of water given to a plant is increased, then the plant height will be decreased.

If IV decreases, then DV increases.

If the amount of water given a plant is decreased, then the plant height will be increased.

Let’s take all of this information and place it on an Experimental Design Diagram:

Experimental Design Frame/Diagram

Title: The Effect of Amount of Water on Plant Height

Hypothesis: If the amount of water given a plant is increased, then the plant height will be increased.

DV: Plant Height

Constants – C: Type of water, type of soil, type of pot

Notes for Chapter 1 – The World of Physical Science

Section 1 – Exploring Physical Science – Focuses on the nature of science, which is a process of gathering knowledge about the natural world. When we make observations of phenomena, we are prompted to ask questions-the beginning of scientific inquiry.

Physical science is defined as the study of matter and energy. It is divided into the study of physics and chemistry. Physics looks at energy and the way that energy affects matter. Chemistry studies the structure and properties of matter and how matter changes.

**Knowledge of physical science is important for many areas of science, such as geology, meteorology, and biology.

Section 2 – Scientific Methods – Scientific methods are the ways in which scientists answer questions and solve problems. There are certain steps that scientists use whenever they are engaged in scientific inquiry. First, an observation is made – this is any use of the senses to gather information (for example, noting that the sky is blue, or that a cotton ball feels soft). Scientists are then led to ask questions about their observations. After gathering preliminary information, scientists are then ready to form a hypothesis – a possible explanation or answer to a question. A good hypothesis is always testable. In other words, information can be gathered or an experiment can be designed to test the hypothesis. Scientists then make a prediction of what they think will happen before testing the hypothesis. One way to test a hypothesis is to do a controlled experiment, which compares the results from a control group with the results from experimental groups. Pieces of information obtained through experimentation are called data. After testing a hypothesis, it is important to analyze your results by using calculations, tables, and graphs. Then, after analyzing your results, you should draw conclusions about whether your hypothesis is supported. Finally, communicating your results allows others to check or continue your work.

Section 3 – Scientific Models – A model is a representation of an object or system. There are three kinds of scientific models: Physical, mathematical, and conceptual. A physical model might be a model space shuttle, or the human eye. Mathematical models are made up of equations and data, and sometimes use computers. Conceptual models are often ideas; for example, the big bang theory is a conceptual model. Some models are smaller than the objects they represent (i.e., globes, solar system models), while other models are larger than the objects they represent (i.e., molecules, DNA). A scientific theory is an explanation for many hypothesis and observations. A scientific law summarizes experimental results and observations. The different between the two is that a theory is an explanation of why something happened the way it did, and a law is a statement that tells how things work.

Section 4 – Tools, Measurement, and Safety – A tool is anything that helps you do a task. Scientists use many tools to help them in their experiments. One way to collect data is to take measurements. But to do this, you need the proper tools. Stopwatches, metersticks, and balances are some tools that can be used to make measurements. (See metric information posted on 9/19 for detailed information on the International System of Units (SI), or metric system).

Length, volume, mass, and temperature are types of measurement used in science. The meter is the basic SI unit of length. Mass is the amount of matter in an object, and the kilogram (kg) is the basic unit for mass. The kilogram is used to describe the mass of large objects, and the gram is used to measure the mass of smaller objects. Volume is the amount of space that something occupies. Liquid volume is expressed in liters (L). Liters are based on the meter. A cubic meter is equal to 1,000 L. Volumes of solid objects are expressed in cubic meters. If you measure the mass and volume of an object, you have enough information to measure its density – the amount of matter in a given volume. Density is called a derived quantity because it is found by combining the two basic quantities of mass and volume. The equation that relates density to mass and volume is:

D = --------

The temperature of a substance is a measurement of hot or cold the substance is. Degrees Fahrenheit and degrees Celsius are often used to describe temperature. The SI unit for temperature is the Kelvin (K).

You will frequently encounter different safety symbols and rules when engaging in scientific investigations. Always pay attention to any safety labels on the sides of chemicals or other equipment – these alert you to what precautions you need to take, such as wearing goggles or gloves.

Notes for Chapter 2 – The Properties of Matter

Section 1 – What is Matter? – Matter is anything that has mass and takes up space. The amount of space take up, or occupied, by an object is known as the object’s volume. The volume of liquids is most often expressed in the units liters (L) and milliliters (mL). A graduated cylinder is used to measure the volume of a liquid. Because the surface of a liquid in any container is curved, to properly read the volume of a liquid in a graduated cylinder one must look at the bottom of the curve of the meniscus (see p. 39 in text). To measure the volume of a solid object, the units must be expressed in cubic units (‘cubic’ means having three dimensions). A block of wood, therefore, has three dimensions – height, width, and length. To find the volume of such an object, one simply multiplies these three dimensions:

V = l x w x h

So the block of wood might have a length of 14 cm, a width of 5 cm, and a height of 3 cm. Multiplying each of these values gives one the volume of the block of wood. Or, a graduated cylinder can be used to measure the volume of a solid object by water displacement – subtracting the water level after an object has been dropped into a graduated cylinder from the original water level. So, if a graduated cylinder is filled to the 80 mL line, and a small lead weight is dropped in, the water line might rise to 120 mL. So to find the volume of the lead, one simply subtracts new from original:

V = 120 mL – 80 mL = 40 cubic centimeters

Mass is the amount of matter in an object. Weight is the measure of the gravitational force exerted on an object. Going to the moon won’t change your mass, but your weight will be 1/6 of what it is on the Earth, because the moon is 1/6 the size of Earth, and therefore it will exert a much weaker gravitational pull on an object at its surface. Inertia is the tendency of an object to resist a change in its motion. So, an object at rest will stay at rest unless acted on by an outside force, and an object moving will keep moving at the same speed and direction unless something acts on it to change its speed or direction. Inertia is the tendency of an object to resist a change in its motion – an object will remain at rest until something causes it to move. Likewise, a moving object will keep moving at the same speed and in the same direction unless something acts on it to change its speed or direction. A more massive object will therefore have greater inertia – pushing a loaded grocery cart is harder than pushing an empty one.

Section 2 – Physical Properties – A physical property of matter can be observed or measured without changing the matter’s identity. So, you don’t have to change an orange’s identity to see its color or measure its volume. Density is one physical property that describes the relationship between mass and volume, and is found by the formula:

D = ______

Other physical properties include conductivity, state, solubility, ductility, and malleability. Physical changes do not produce new substances – crushing a can, tearing a piece of paper, or melting an ice cream bar are all physical changes – no change to the original substance (in terms of its chemical makeup) was made – it’s still a can, a piece of paper, and an ice cream bar – only its size or appearance has changed, or state.

Section 3 – Chemical Properties – Chemical properties describe matter based on its ability to change into new matter that has different properties. Some chemical properties include flammability – the ability of a substance to burn - and reactivity – the ability of two or more substances to combine and form one or more new substances. Burning paper produces heat and smoke – new substances. An iron nail can react with oxygen in the air to form iron oxide, or rust – these are examples of chemical changes – when one or more substances are changed into new substances that have new and different properties. These two terms are not the same – chemical properties of a substance describe which chemical changes will and will not occur. Chemical changes are the process by which substances actually change into new substances. The key question to ask when trying to determine whether a physical or chemical change has occurred is: Has a new substance been formed? Did the original composition change? Many physical changes can be reversed – an ice cube that has melted can be turned back into solid ice by freezing the liquid water again. However, most chemical changes are not easily reversed.

Notes for Chapter 3 – States of Matter

Section 1 – Three States of Matter – The three states of matter that we will focus on are solid, liquid, and gas (a fourth state, plasma, occurs at very high temperatures, such as those found within stars like the Sun. Electrons are stripped away from their parent atoms in a plasma). States of matter are the physical forms in which a substance can exist. Water, for example, commonly exists in three states: solid (ice), liquid (water), and gas (steam). Solids have a definite shape and volume. There are two kinds of solids – crystalline and amorphous. Crystalline solids have a very orderly, 3-D arrangement of particles (ex. Diamonds, iron and ice). Amorphous solids are made of particles that do not have a special arrangement (ex. Glass, rubber and wax). Liquids have a definite volume, but they take the shape of the container that they are in. A special property of liquids is surface tension – a force that acts on the particles at the surface of a liquid. This is what causes some liquids to form spherical drops like dew on grass. Another important property of liquids is viscosity – a liquid’s resistance to flow. Generally, the stronger the attraction between molecules that make up a liquid, the more viscous it is (honey has a higher viscosity than water). Gas is the state of matter that has no definite shape or volume. The particles of a gas move quickly, so they can break away completely from one another. The particles of a gas move quickly, so they can break away completely from one another. So the particles of a gas have less attraction between them than do particles of the same substance in the solid or liquid state.

Section 2 – Behavior of Gases – Gases behave differently from solids or liquids, in that the particles that make up gases are spaced widely apart. To understand gas behavior, we have to understand the relationship between temperature, volume, and pressure. Temperature is a measure of how fast the particles in an object are moving. If you take a balloon and put it outside on a hot day, you will notice that the balloon will expand. This is because the heat will causes the particles in the balloon to move faster – they collide with the inner walls of the balloon with greater force, causing the balloon to grow in size. But on a cool day, the particles of gas in the balloon have less energy, and so do not push as hard on the walls of the balloon. Volume is the amount of space that an object takes up. Because the particles of a gas are spread out, the volume of any gas depends on the container that the gas is in. Gas particles can be compressed much more easily than particles of a liquid, which is why you can bend and twist a balloon filled with air, but you cannot do so with one filled with water – the balloon would break! Pressure is the amount of force exerted on a given area of surface. You can also think of it as the number of times the particles of a gas hit the inside of their container. A basketball has a higher pressure than a beach ball because inside the basketball, there are more particles of gas in it, and they are closer. The particles collide with the inside of the ball at a faster rate. The beach ball has a lower pressure, on the other hand, because there are fewer particles of gas, and they are farther apart. The particles in the beach ball collide with inside of the ball at a slower rate, thereby leading to lower pressure.

Robert Boyle, a 17^th century Irish chemist, described the relationship between the volume and pressure of a gas. Boyle’ Law states that the volume of a gas is inversely proportional to the pressure of a gas when temperature is constant (see Fig. 3 on p. 72). So as pressure increases, the volume of a gas decreases, and as pressure is decreased, the volume of a gas increases. Charles’ Law states that the volume of a gas is directly proportional to the temperature of a gas when pressure is constant (see Fig. 4 on p. 73). So decreasing the temperature of a gas causes the particles to move more slowly, thereby leading to a decrease in volume. Increasing the temperature of the gas causes particles to move more quickly, thereby leading to a greater volume.

Section 3 – Changes of State – A change of state is the change of a substance from one physical form to another (ice to liquid to gas, for example). All changes of state are physical changes – the identity, or chemical composition never changes. The particles of a substance move differently, and have different amounts of energy, depending on what state it is in. Particles in liquid water have more energy than particles in ice, and so move faster. Particles in steam have more energy still, and so move even faster. In order to change a substance from one state to another, energy must be added or removed. Melting is the change of state from solid to liquid. By adding energy to an ice cube, for example, the temperature of the ice cube is increased, and the ice particles move faster. When a certain temperature is reached, the ice will melt. A substance’s melting point is that temperature at which the substance changes from a solid to a liquid. For a solid such as ice to melt, particles must overcome some of their attractions to each other. When a solid is at its melting point, and energy added to it is used to overcome the attractions that hold the particles in place. So melting is an endothermic reaction – because energy is gained by the substance as it changes state.

Freezing is the change of state from a liquid to a solid. The temperature at which a liquid changes into a solid is the liquid’s freezing point. Freezing is the reverse process of melting; thus freezing and melting occur at the same temperature (see Fig. 3, p. 75). So if energy is added at 0 degrees Celsius, the ice will melt, because any energy added goes into breaking the bonds of attraction of the particles. If energy is removed at 0 degrees Celsius, the liquid will freeze, because removing energy will cause the particles to begin locking into place. So freezing is an exothermic reaction, because energy is removed from the substance as it changes state.

Evaporation is the change of a liquid to a gas. It is possible for evaporation to occur at the surface of a liquid that is below its boiling point (leave a glass of water out and you will notice that the water eventually evaporates). So in the process of evaporation, some particles at the surface of the liquid move fast enough to break away from the particles around them and become a gas. Boiling is the change of a liquid to a vapor, or gas, throughout the liquid (see Fig. 4, p. 76). This is an important point – evaporation occurs at the surface of a liquid, and boiling occurs throughout the liquid. Boiling occurs when the pressure inside the bubbles (called vapor pressure) equals the outside pressure on the bubbles (called atmospheric pressure). The temperature at which a liquid boils is its boiling point. Water boils at 100 degrees Celsius at sea level. However, in Denver, about 1.6 km above sea level, the atmospheric pressure is lower, since there is less air above you. Therefore, since there is less atmospheric pressure, the boiling point of water will be slightly less – about 95 degrees Celsius.

Condensation is the change of state from a gas to a liquid. Condensation and evaporation are the reverse of each other. The condensation point of a substance is the temperature at which the gas becomes a liquid. And the condensation point is the same temperature as the boiling point at a given pressure. Sublimation is the change of state in which a solid changes directly into a gas. Dry ice (solid carbon dioxide) is much colder than ice made from water.

When most substances gain or lose energy, one of two things happen to the substance: its temperature changes or its state changes. The temperature of a substance, remember, is a measure of the speed of the particles that make up the substance. So when the temperature of a substance changes, the speed of the particles also changes. But the temperature of a substance does not change until the change of state is complete. For example, the temperature of boiling water stays at 100 degrees Celsius until it has all evaporated (see Figure 7, p. 79).

Notes for Chapter 4 – Elements, Compounds, and Mixtures

Section 1 – Elements –

• An element is a pure substance that cannot be separated into simpler substances by physical or chemical means.

• A pure substance is a substance in which there is only one type of particle.

ex. – a sample of gold is a pure substance, since every atom in the sample is like every other gold atom.

Properties of Elements -

• Each element has its own characteristic properties

• Physical properties would include such things as melting point, density, and boiling point.

• Chemical properties would include reactivity with another substance, flammability, etc.

• Elements may share properties with other elements (ex.-helium & krypton are both unreactive gases but have different densities)

Identifying Elements by Their Properties –

• Each element can be identified by its own unique properties

• Examples of element identification by chemical properties – zinc is reactive with acid; hydrogen and carbon are flammable

• Examples of element identification by physical properties – sulfur is yellow (color), aluminum is malleable

Classifying Elements by Their Properties –

• Elements are grouped into categories by the properties they share

• Elements are classified as metals, nonmetals, or metalloids

Metals –

• Metals are shiny, and conduct heat and electric current

• Metals are also malleable (can be hammered into thin sheets), and ductile (can be drawn through a wire)

• Examples of metals are lead, copper, and tin.

Nonmetals -

• Nonmetals do not conduct heat or electric current, and solid nonmetals are dull (not shiny) in appearance, and may be brittle and unmalleable.

• Examples of nonmetals are iodine, sulfur, neon, and xenon.

Metalloids –

• Metalloids have properties of both metals and nonmetals – some are shiny, some are dull.

• Metalloids are somewhat malleable and ductile.

• Some metalloids conduct heat and electric current well, but some do not.

• Examples of metalloids include boron, antimony, and silicon

Section 2 – Compounds – A compound is a pure substance composed of two or more elements that are chemically combined.

• There are many examples of compounds that we encounter every day. The elements sodium and chlorine, for example, combine to form table salt – sodium chloride. Iron and oxygen combine to form rust – iron oxide.

• Compounds can be identified by their physical properties (melting point, density, color, etc.), as well as chemical properties (reactivity with acid, reactivity to light, etc.).

• It is important to understand that a compound has properties that differ from those of the elements that form it. For example, take sodium chloride. When we look at the elements that form it, we have sodium – a soft, silvery-white metal that reacts explosively if brought into contact with water. Chlorine is a poisonous, green gas. But when we chemically combine these two elements, a harmless compound is formed that has unique properties – properties that differ from the elements that formed it.

• Some compounds can be broken down into their elements by chemical changes by applying heat or electric current. For example, you can heat the compound mercury oxide, and a chemical change occurs, causing it to separate into its component elements mercury and oxygen. Other compounds break down to form simpler compounds instead of elements. For example, carbonic acid (found in soda) breaks down into the compounds carbon dioxide and water.

• Compounds are found in nature, but often the compounds found in nature are not the raw materials needed by industry. Ammonia is a common compound used in industry, used to make fertilizers. Combining the elements nitrogen and hydrogen makes ammonia. Many examples of compounds can be found in the natural world. Proteins, for example, are compounds found in all living things. Carbon dioxide is another important compound in nature, and is of central importance in the process of photosynthesis – the means by which plants make food and release oxygen into the atmosphere.

Section 3 – Mixtures – A mixture is a combination of two or more substances that are not chemically combined. So when two or more materials are put together they form a mixture if they do not react chemically to form a compound. For example, cheese and tomato sauce do not react when they are used to make a pizza – so a pizza is a mixture. A salad (with lettuce, tomatoes, onions, etc.) would be another common example of a mixture.

• You can sometimes easily separate mixtures through physical methods – for example, taking mushrooms off of a pizza. Other mixtures are not so easily separated. For example, you can’t pick the salt out of a saltwater mixture. Although you could heat the saltwater mixture, evaporating the water and leaving the salt behind (see p. 99 for other ways to separate mixtures).

• Whereas a compound is made of elements in a specific mass ratio, the components of a mixture do not need to be mixed in a definite ratio. For example, granite is a mixture made of three minerals, feldspar, mica, and quartz. Even though the proportions of these minerals may change, this combination of minerals is always a mixture called granite.

A solution is a mixture that appears to be a single substance. It is composed of particles of two or more substances that are distributed evenly among each other. Solutions have the same appearance and properties throughout the mixture.

• The process in which particles of substances separate and spread evenly throughout a mixture is called dissolving. The solute is the substance that is being dissolved, and the solvent is the substance in which the solute is dissolved. For example, salt water is a solution. Salt is soluble in water, meaning salt dissolves in water. So salt would be the solute, and water the solvent.

• Solutions can be liquids (ex. Gasoline, soft drinks, many cleaning supplies, etc.). However, solutions may also be gases, such as air, or even solids, such as steel. Alloys are solid solutions of metals or nonmetals dissolved in metals (brass is an alloy of the metal zinc dissolved in copper).

• Particles in solutions are so small that they never settle out. They also cannot be removed by filtering (see, for example, figure 4 on p. 101).

• A measure of the amount of solute dissolved in a solvent is concentration. Concentration is expressed in grams of solute per milliliter of solvent (g/mL). Solutions can be described as being concentrated or dilute. These terms, however, do not tell you the amount of solute that is being dissolved. In Figure 5 on p. 102, the two solutions have the same amount of solvent, but one has less solute than the other. Accordingly, one is dilute, and the other concentrated. So a dilute solution will contain less solute, and a concentrated solution will contain more solute.

• The solubility of a solute is the ability of the solute to dissolve in a solvent at a certain temperature. Most solids are more soluble in liquids at higher temperatures, but gases become less soluble in liquids as the temperature is raised.

• A suspension is a mixture in which particles of a material are dispersed throughout a liquid or gas but are large enough that they settle out.

• Some mixtures have properties between those of solutions and suspensions – these mixtures are known as colloids. A colloid is a mixture in which the particles are dispersed throughout but are not heavy enough to settle out. So the particles in a colloid are small and well mixed. Milk, mayonnaise, and whipped cream are all examples of colloids.

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Notes for Quarter 2

Notes for Chapter 5 – Matter in Motion

Section 1 – Measuring Motion –

We often think of the motion of an object as something easy to detect – you just watch the object. But you are actually watching the object in relation to another object that stays in place. When an object changes position over time relative to a reference point, that object is in motion.

Speed is the distance traveled by an object divided by the time taken to travel that distance. To determine average speed, the following equation is used:

Total distance

Average speed = ---------------------

Total time

The SI (Metric) unit for speed is meters per second (m/s). However, kilometers per hour (km/h), feet per second (ft/s), and miles per hour (mi/h) are other units commonly used to express speed.

Velocity is the speed of an object in a particular direction. It is important to remember that speed and velocity are not the same. For example, two birds might leave a tree at the same speed – 10 km/h for 5 minutes, 12 km/h for 8 minutes, and 5km/h for 10 minutes, but not end up in the same place. Why? They went in different directions. So the speeds were the same, but they had different velocities.

Velocity must include a reference direction. To say that an airplane’s velocity is 600 km/h would not be correct. You would have to include a reference direction, such as 600 km/h south. NOTE: See Fig. 3 & 4 on p. 121.

Acceleration is the rate at which velocity changes. Velocity changes if speed changes, if direction changes, or if both change. So, an object accelerates if its speed, its direction, or both change.

• If an object is speeding up, we say that the object has a positive acceleration.

• If an object is slowing down, we say that the object has a negative acceleration.

• You can find the average acceleration by using the equation:

Final velocity – starting velocity

Average acceleration = ----------------------------------------------

Time it takes to change velocity

*The SI (Metric) units for Acceleration:

• Velocity is measured in meters per second (m/s)

• Time is measured in seconds (s)

Final velocity – starting velocity m/s

Average acceleration = ---------------------------------------------- -----

Time it takes to change velocity s

• The units are meters per second ÷ second which is meters per second per second or meters per second squared.

• The SI unit meters per second per second mean that an object speeds up by a certain velocity every second.

• Example: If a cyclist speeds up to 5m/s2 from 1 m/s2 in 4 s, they have increased their speed by 1 m/s every second, or have an acceleration of 1 m/s2.

NOTE: See Fig. 5 on p. 122.

Section 2 – What is a Force?

• In science, a force is simply a push or a pull. Put in a more detailed way, a force is a push or pull exerted on an object in order to change the motion of the object.

• Forces cause changes in three things:

– Shape

– Direction

– Speed (causing acceleration or deceleration)

The SI unit for force is the Newton (N). This unit is names after the famous scientist Sir Issac Newton.

Usually, more than one force is acting on an object. The net force is the combination of all forces acting on an object. To determine the net force on an object if all forces act in the same direction, you add the two forces together. If one person pushes with a force of 25N and the other pulls in the same direction with a force of 20N, then you simply add these numbers to find the net force (25N + 20N = 45N). See Fig. 3, p. 125. If the two forces are opposing one another, as the two dogs pulling on a rope in Fig. 4 p. 126, then you subtract the two opposing forces: 12N – 10N = 2N.

Forces act on all objects at all times. They can be balanced or unbalanced. Balanced forces will not cause a change in the motion of a moving object. Why? Because when the forces on an object produce a net force of 0N, then the forces are said to be balanced (See Fig. 5, p. 126). On the other hand, when the net force on an object is not 0N, then the forces on an object are unbalanced (See Fig. 127, p. 127).

Section 3 – Friction- A Force That Opposes Motion

Friction is a force that opposes motion between two surfaces that are in contact. Basically, when the microscopic hills and valleys of one surface stick to the hills and valleys of another surface, friction is created.

Rougher surfaces have more microscopic hills and valleys than smooth surfaces do. So the rougher the surface is, the greater the friction.

There are two types of friction. If you slide a stack of books across a table, you are witnessing kinetic friction. Kinetic means “moving,” so the amount of kinetic friction between two surfaces depends in part on how the surfaces move. Surfaces can slide past each other, or a surface can roll over another surface. Usually, the force of sliding kinetic friction is greater than the force of rolling kinetic friction – which is why it’s easier to move a piece of heavy furniture on wheels rather than just sliding it across the floor (See Fig. 3, p. 130). When a force is applied to an object but does not cause the object to move, static friction occurs. Static means “not moving.” Suppose you try to push a stack of heavy books across a table with your finger. The books don’t move because the force of static friction balances the force applied by your finger (See Fig. 4, p. 131).

Friction can be both helpful and harmful. Without friction, the tires on your car could not push against the ground to move the car forward, and the brakes could not stop the car – so this is a good example of friction being helpful. On the other hand, friction between moving engine parts causes the parts to eventually wear down, so this is an example of friction being harmful.

Friction can be reduced. You can reduce the amount of friction by using lubricants such as oil, wax, or grease. Friction can also be reduced by switching from sliding kinetic friction to rolling kinetic friction (as in

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