To Begin: http:/phetcolorado.edu -> HTML 5 SIMs -> Forces and Motion Basics or link belowhttps://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html

Activity assignment was prepared byScott Clements and was published in PHET site.

Note: These simulation does not show the weight and normal force (a.k.a support force) acting on the box/crate by the skateboard. They are equal in size and the normal force on the box/crate is acting vertically upward and the weight is vertically downward.

Part I - Newton's First Law

Choose the "Friction" window to start the simulation and move Friction slide bar to None

Make sure the boxes that say "Force", "Values" and "Speed" are checked!

1. Apply a force of 50 N right to the box. Describe the motion of the box using physics terms (i.e. velocity, acceleration, displacement). Refer to the speedometer in your answer.

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1. Reset the scenario and stop the play button (don't forget to check forces, speed again). Apply a force of 50 N to the right for about 5 seconds then reduce the applied force to zero (the man should stop pushing). Don't reset the scenario. Describe the motion of the box. Refer to the speedometer in your answer.

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1. Explain the exact steps needed to make the box come to a stop.

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Summary

Newton's First Law of Motion States "An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force." Explain how your observations in a - c support this Law.

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Part II - Newton's Second Law

1. Reset the sim, don't forget to check force, values and speed again and move Friction slide bar to None. Remove the box and place a garbage can on top of the skateboard. Using your timer/phone, measure the amount of time it takes to reach maximum speed using a force of 50 N. Try this again with forces of 100N, and 200N. 3pts

Applied Force (N)	Time To Max Speed (s)
50	Answer
100	Answer
200	Answer

1. Reset the sim, check force, values, speed and the masses boxes this time. Set the applied force to 200 N Right. Using your timer/phone measure the amount of time it takes to reach maximum speed. Repeat with two crates, one crate and a garbage can, and a refrigerator. Record your findings! What is the maximum speed shown on the screen? _________

Object - Mass (kg)	Time To Max Speed from zero speed (s)	Calculate the acceleration (m/s2)
50	Answer	Answer
100	Answer	Answer
150	Answer	Answer
200	Answer	Answer

Note: Acceleration = Change in velocity / given time

Summary

Newton's Second Law states "The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object." Explain how your observations in both a and b support this Law.

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Part III - Friction's Effects

The behavior of the skateboard in Part I and part II were not very realistic because friction was not present. Because we did the experiment without Friction.

Now Reset all and stop the play button.check only the speed box and set friction bar to None.

1. Apply a force to get the box to about half of it's maximum speed, then remove the force.
2. While the box is moving, move the friction slider to 1/2 way.

What happened to the box? Explain in terms of speed.

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Summary

Is friction a force? What evidence do you have? Check forces box to verify your evidence.

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Part IV - Back to Newton's Second Law

Reset all. Make sure Forces and Speed are checked and Friction slider should be at the midpoint of the Friction scale.

1. Apply a force of 50 N. Describe the movement of the box.
2. Apply a force of 100 N. Describe the movement of the box.
3. Apply a force of 150 N. Describe the movement of the box.
4. Check the box that says "Sum of Forces". Repeat procedures a, b, and c. What was different about c?

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Summary Newton's Second Law states "The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object." Explain how your observations in part IV experiment relate to the underlined portion of this Law (hint, you might want to look up the definition of the word "net").

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Part V: Friction in Detail

1. Reset the app. Check the force and speed box. Friction slider is at the midpoint on the scale. Apply 50 N of force to the crate. Slowly click (in 50 N increments) to increase the amount of applied force until the crate starts to move/accelerate. Note the range of force values when the crate first started to move. Record this range below (e.g. starts moving somewhere between 0 and 50 N).

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1. Reset the app. Repeat the steps in "a". Once you have just made the crate move do not adjust the force any higher. Allow the block to move with this constant force for 2.0 seconds. Now reduce the force by 50 N. How does the crate behave immediately after reducing the force by 50 N? Did it keep accelerating? Move at a constant speed or decelerate? Does this behaviour surprise you based on your knowledge of Newton's 1^st and 2^nd Law. Why do you think the crate behaves this way?

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1. Reset the app. Check the speed, force, sum of forces and values boxes. Adjust the value of the applied force using single Newton increments to determine the exact force required to make the crate move. Mentally note the value of this force so you can record it after in the space below. Now keep increasing the value of the applied force in large 50 N or small single Newton increments. What happens to size of the friction force? What is the value of the friction force now? Why does the friction force behave this way?

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1. Repeat step c and after the block has accelerated for 3.0 seconds reduce the applied force to 0 N. What happens to the size of the friction force after the applied force goes to 0 N? How does the crate behave?

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1. Reset the app. Check the forces, values and speed boxes. Place another crate on top of the first. Determine the minimum amount of force required to move the crates. Determine the minimum amount of force required to keep the blocks moving at a constant speed. Record these below:

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1. How do these values compare to the values found for one crate? What does this tell you about the affect of mass on friction?

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1. Reset the app. Check the force and values boxes. Apply 50 N of force to the crate. What is the value of the force of friction now? Record this. Increase the applied force and note how the friction force behaves. Record this behaviour in the space below.

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Summary

Make four or more general statements about the force of friction based on your observations in parts a - f.

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