## Due 3:30 pm, Tuesday, September 15th

Physics 105, Fall Term, 2009

Did you complete the reading assignment?

Yes
No

## KEY CONCEPTS:

1) An object will continue in its state of motion (moving or at rest) unless acted upon by a force.

2) The net force on an object is the product of the mass of the object and its acceleration.

3) Every force is opposed by a force that is equal in magnitude but opposite in direction.

All science is based on Newton's 3 laws of motion. Before Newton described nature in these laws, "science" was referred to as natural philosophy and was based on the belief of philosophers' ideas on how elements desire to interact with each other. Now, several hundred years after Newton, we observe the behavior of nature as reactions to forces applied to them.

Go to the applet at: http://phet.colorado.edu/sims/forces-1d/forces-1d_en.jnlp where we will observe Newton's laws.

## Newton's 1st Law

Click the friction 'Off' bubble and check the 'Barriers' check box on the right side of the applet.

Before applying a force to the file cabinet, watch it for a while as it is at rest. Does it change its state of motion?

Yes
No

Now apply a large force to the cabinet for a short moment by clicking on it and quickly dragging it with the mouse to the right or left and then releasing the mouse. For the short period of time that the motion is applied, does its state of motion change?

Yes
No

After the file cabinet is released from the force applied to it, does its state of motion change?

Yes
No

Eventually the file cabinet stops when it hits the brick wall. Why, in physics terms, does the file cabinet stop moving?

Newton's 2nd Law

Now instead of manually applying force with the mouse, set a constant application of force by typing in a force in the 'Applied Force' box on the left side of the applet and then pressing the 'Go' button. Select the 'Graph Applied Force' and 'Graph Acceleration' buttons. You can also select which object you are applying the force to by selecting them from the right side of the applet. To reset the position and graphs press the 'Clear' button on the left side of the applet.

Apply a constant 100 N force to each object and watch its motion and the applied force graphs and acceleration graphs. Which object has the most applied force on it according to the graph?

File Cabinet
Refrigerator
Text Book
Crate
Sleepy Dog
All the same

Which object has the greatest acceleration according to what you see and what is on the graph?

File Cabinet
Refrigerator
Text Book
Crate
Sleepy Dog
All the same

Explain your result from the question above.

What is the acceleration of each object after they hit the wall? What is the net force on the object?

Newton's 3rd Law

When an object is being pushed against a wall, the force being applied on that object is now being applied on the wall. If this is the case, why does the wall not move?

Using the values you did for the activities for Newton's 2nd law, how much force does the wall put on the object when it is being pushed into the wall?

0 N
50 N
100 N
200 N

How much force does the object put on the person pushing it while it is still moving (before it hits the wall)?

0 N
50 N
100 N
200 N

FEEDBACK

The comments entered in these last two boxes go into a big anonymous data file that I will use to guide the lectures of the day. That means two things:

1) If you have a specific question or concern and would like an individual answer you will need to come by the office or send an email.
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Was there anything that you didn't understand in the reading assignment?  What was confusing to you?