“Push that thing!” Net Forces in 1D PhET Simulation
Newton’s Second Law w/o Friction
Select various objects and notice how their acceleration and velocity change with changing mass
and force. Recall that acceleration is how velocity changes.
1. When acceleration and velocity vectors are in the same direction, the object is _______________ ______
2. When a and v vectors are in opposite directions cause an object to ______________ ____________.
3. When net force is zero, acceleration is _______________ and velocity is ____________________
Complete the table below
Force applied Mass (fridge)
Acceleration
Force applied
Mass (crate)
100. N
200. kg
25. N
50. kg
400. N
200. kg
75. N
50. kg
200. kg
1.5 m/s2
Acceleration
.75 m/s2
50. kg
Determine the mass of the unknown object. Show your work.
________ kg
Newton’s Second Law w/ Friction
Familiarize yourself with the simulation with friction.
1. What do you notice about the values of the friction force vectors compared to the values of the applied
force vectors?
________________________________________________________________________________
2. Discuss the direction of the friction force.
________________________________________________________________________________
3. Discuss the magnitude of the friction force as the applied force becomes greater.
________________________________________________________________________________
4. Can the friction force ever be larger than the applied force? ___________ Defend your answer.
________________________________________________________________________________
Complete the following table. Please use colored, bold font for your responses.
Applied Force, N Friction Force., N
Mass
Acceleration m/s2
250. N
150. N
175. N
175. N
125. N
125. N
0.0 m/s2
0.5 m/s2
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Consider the diagram here. Determine the value of…
Friction Force
Applied Force
Net Force
Mass
Acceleration
Fill in the table below with a calculator then check your work with the simulations (no friction).
Force applied
Mass (fridge)
acceleration
800. N
200. kg
50. N
200. kg
1000. N
200. kg
Force applied
Mass (water)
25. N
100 kg
100 kg
200. N
100 kg
Force applied
Mass (large book)
5. N
10.0 kg
20. N
10.0 kg
acceleration
2.0 m/s2
acceleration
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10.0 kg
4.0 m/s2
Force applied
Mass (crate)
acceleration
100. N
50. kg
300. N
50. kg
50. kg
2.5 m/s2
Conclusion Questions:
SHOW WORK when doing math
1. On a static crate, friction was larger than / smaller than / equal to the applied force.
2. Our experiment showed that static (not moving) friction is greater than / less than kinetic (moving)
friction.
3. I’m not accelerating, so the net (vertical) force on me, while I’m sitting here doing this lab is ___________.
4. Without friction, applying a constant force produces a decreasing / constant / increasing acceleration.
5. Without friction, applying a constant force produces a decreasing / constant / increasing speed.
6. While coasting (no applied force) without friction, the acceleration is ________________ and velocity is
________________.
7. When a force of 300. N is applied to an object that experiences 200. N of friction the net force that will
cause acceleration would be ________________.
8. A 150. kg refrigerator is held to the ground with a maximum of 800. N of friction force. If you apply an
increasing amount for force every second from 100. N to 1000. N, sketch what a graph of friction force
overtime might look like as you push on the fridge (and continue to push it after it starts moving).
9. Imagine you push a 50.0 kg crate with 200. N of force. If friction pushes back with 100. N of force, the
crate will accelerate with a magnitude of
_______________ m/s2.
10. A crate with a sliding velocity of 10.0 m/s has a mass of 75.0 kg. If it encounters 100. N of friction force
(without an applied force), how long will it take to stop moving?
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________________ s
11. A student mentions that if friction force is larger than applied force, a non-moving crate would not move.
Discuss the pros and cons of this statement.
_______________________________________________________________________________________
12. Another student claims that if there are no forces pressing against a moving car, that car will continue at a
constant speed. Discuss your agreement or disagreement with this statement.
_______________________________________________________________________________________
13. Aristotle wrote about “natural motion.” In his views, the moon naturally moves around the earth, so no
push or pull is required for the moon to orbit around the earth. Similarly, a thrown rock naturally moves
towards the earth, so no push or pull is required for it to fall. Discuss Aristotle’s theory and your
agreement or disagreement with it.
_______________________________________________________________________________________
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