GRADE: Seventh

CONTENT STANDARD: Physical Science

CONTENT TOPIC: Motions and Forces

CONCEPT: Matter and energy in the universe are governed by physical laws.

CONTENT OBJECTIVE: 7B1.00 To understand the laws of motion

INSTRUCTIONAL OBJECTIVES: The learner will:

1.01 define friction.
1.02 explain the property of matter called inertia.
1.03 state the first law of motion or law of inertia.
1.04 explain what happens when a force is exerted on an object that is in equilibrium.
1.05 state the second law of motion.
1.06 state the third law of motion.
1.07 define data.
1.08 collect a set of data from a simple experiment.
1.09 plot the data collected on a graph.
1.10 draw a conclusion based on the data.

OUTLINE OF CONTENT:

I. Friction
A. Definition
B. Examples
II. First Law of Motion
A. Also called Law of Inertia
B. Definition
C. Example
III. Second Law of Motion
A. Definition
B. Formula
C. Example
IV. Third Law of Motion
A. Also called Law of Action and Reaction
B. Definition
C. Example
V. State the problem
VI. Experiment
VII. Observe
A. Using senses
B. Using measurement
VIII. Record Data
IX. Analyze
A. Compare data with others in class
B. Relate data to unknown facts
X. Interpret
A. Graph data
B. Form conclusions

TN COMPONENT OF SCIENCE: Unifying Concepts of Science

TN GOAL:

To enable students to acquire scientific knowledge by applying concepts, theories, principles and laws from life/environmental, physical, and earth/space science.

2.1 SCALE AND MODEL - The development of models provides a conceptual bridge between the concrete and the abstract, while the use of scales allows for a comparison of differences in magnitude between the model and the desired form.

2.1a A model is a representation used to simplify complex phenomena.

BENCHMARK: Models are often used to represent concepts of various magnitudes.

2.1d The scale chosen for a model determines its effectiveness.

BENCHMARK: The usefulness of a graph paper drawing is determined by the scale utilized.

TIME REQUIRED:

1 - 1 1/2 hours depending on depth

Box filled with wooden blocks, empty tin cans, balloons, spring scales

Force, friction, inertia, newton Classroom Connector One

Sir Isaac Newton discovered three important laws of motion. These laws are the topic of our discussion today.

Forces are very important to our world because they affect all of our movements. A force is a push or a pull. Another force which affects our motion is friction. Friction is often helpful. An example is when we put snow tires on our car to gain traction. Friction is harmful when it slows our movement by increasing the force needed to move an object. An example of harmful friction is trying to push a load of bricks across a very rough surface.

Newton's first law of motion is also called the Law of Inertia. Inertia is the tendency an object has to resist a change in motion or position. All matter has inertia. Your inertia will keep you sitting in your seat unless a force pushes you out or you voluntarily decide to move. The first law states that an object at rest will remain at rest or an object in motion will remain in motion unless acted upon by an outside force. An example of this law is a car traveling down the road at 45 mph with you as the passenger. The driver suddenly applies the brakes and you move forward toward the dash continuing in the direction in which you were moving.

The second law of motion concerns the amount of mass of the object and the amount of force. It states that the greater the mass of an object, the greater the amount of force needed to move the object. In addition, the greater the mass, the less the acceleration of the object once it moves. This law has the formula which says force equals mass time acceleration. The unit of force is the newton (named after Sir Isaac Newton) which equals a 1 kilogram mass moving at a speed of 1 meter per second every second. Here is an example of Newton's second law: Imagine two shopping carts, one empty and the other one full. Which cart takes more force to get it in motion? (Full cart)

The third law of motion is probably the most popular of the three laws. It is also called the Law of Action and Reaction. This law states that for every action there is an equal, but opposite, reaction. There are numerous examples of this law. For example, when you fire a gun, the bullet goes in one direction, and the gun goes backward in the opposite direction.

1. To demonstrate the first law of motion have students push a box of blocks over a smooth surface such as a table, or tile floor. Then have them push the same box over a rough surface such as a sidewalk, or driveway. Which takes more force? (Box of blocks on a rough surface) Have them set the box on empty cans to simulate wheels and repeat the process.

2. To demonstrate the second law of motion have students attach a spring scale to an empty box first and pull along the floor for a distance of 5 meters. Then fill the box with books or blocks and have students repeat the process. This could be done several times varying the number of blocks or books and the results could be graphed. (Let the number of books be X axis and Force in newtons be the y axis.)

3. To demonstrate the third law of Motion, blow up a balloon but do not tie the end. Release the balloon and have students explain how this demonstration illustrates the third law.

(Provide students with a ditto sheet of problems to work using F = a.)

Example: Determine the amount of force necessary to accelerate a 1500 kilogram car at a rate of 15 m/s².
F = ma
F = 1500 Kg x 15 m/s²
F = 22,500N (newtons - Remember 1N = 1 Kgm/s²)

(Have students classify a list of examples for the laws.)

Examples:
a. stepping from boat to shore (3rd law)
b. the funny feeling in your stomach when the elevator moves too quickly (1st)
c. A 50 pound boy and a 150 pound man sit on the floor. Which takes more force to move? (2nd))

Today we have studied about Newton's Laws of Motion. Write an example of your own for each law.

Classroom connector Two

One hour

Thermometers, beakers or glasses, ice, salt (If Celsius thermometers are not available small outdoor Fahrenheit thermometer could be used.), time with second hand or stop watch

Data, hypothesis

Every scientist must know how to search for answers to questions, perform experiments and analyze his/her data. We are going to become scientists today and investigate a problem.

The first step to studying a problem is to state the hypothesis. A hypothesis is an educated guess which predicts what you believe might happen.

Then you want to perform several experiments to try to prove or disprove your hypothesis. During the experiments it is vitally important that you make several observations of what occurs. These observations can be done using the five senses (except we never taste anything in the laboratory) or by measurements or preferably both. Measurements might include size, temperature, volume, etc.

The observations you make are called data. It is important that you record on paper the data taken during an experiment. From the data you collect and that collected by others, you should be able to form a conclusion that will either support or not support your hypothesis. It is okay if your hypothesis is incorrect, scientists do not always answer a problem with the first experiment.

Students are going to do an experiment that answers the question: why do we put salt on the streets when it snows?

(Divide the class into groups depending on how many thermometers and glasses or beakers you have. Have all students do the following experiment:

1. Put a specified amount of water into the first glass or beaker. Take the initial temperature. Record.

2. Set the glass down into a much larger container. Surround it with ice and add some salt to the water. Place the thermometer into the water.

3. Place the thermometer into the water.

4. Record the temperature every minute until the water freezes.

5. Graph the data and draw the curve.

6. Form a conclusion using your data. (Conclusion: salt lowers the freezing point of water)

This same experiment could have several variations. Keeping the amount of water always constant, vary the amount of salt for each group. Graph data and compare. Secondly if students are capable; have them record temperature every 30 seconds. This gives more data.

Effect of salt on the freezing point of water

Temperature C⁰

40

O

20

10


1

2

3

4

5

Time (minutes) or (seconds)

(Students will find that the more salt added, the lower the freezing point will be.)

On a sheet of paper, tell why you think it is important to record the observations and measurements you make.

data - facts obtained from experimentation

force - a push or pull

friction - a force that oppose motion

hypothesis - educated guess

inertia - tendency of an object to resist a change in position or motion

newton - a unit of force equal to 1 Kgm/s²

This is the time this file has been accessed since 04/02/98.

The University of Tennessee at Martin is not responsible for the information or views expressed here.

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