"Forces and Motion Basics" Physics

Newton’s Laws of Force and Motion

Goals: Explore Newton’s Laws of Force and Motion

Requirements:

• Please read the section(s) in your text two-dimensional motion and Newton's Laws.

• A stop watch (Tip: mobile phones come with a stopwatch app.) Background: Newton’s second law of motion states that the acceleration a of an object or system

is directly proportional to the unbalanced or net force Fnet action on the system and inversely proportional to the total mass m of the system, i.e.,

𝒂 = 𝑭𝑵𝒆𝒕

𝒎

This relationship will be investigated by analyzing forces in one dimension -- applied,

frictional, and total.

Click here to bring up the laboratory activity in another window

If the above link does not work, please copy the following URL into a browser: https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html

You should see this:

Exercises:

1. Setup a. Click on Net Force and you should see

Newton’s Laws of Force and Motion

b. Make sure the following boxes are checked (upper right in lab) i. Sum of Forces ii. Values iii. Speed

2. Net Force

In this activity we study Net Force; that is, what is the resultant force after adding all forces (the sum of forces).

Select the tallest blue person and put the person on a knot on the left. Similarly, select the tallest red person and put the person on a knot on the right. a. Click Go!

i. Question # 1: What is the net force? ii. Question # 2: Does it matter where the person is on the rope; i.e., knot 1, 2, 3,

or 4? iii. Question # 3: Regarding Questions # 2, why does it not matter where the

person is on the rope?

Click Return Replace the red person with the two smallest red persons b. Click Go!

i. Question # 4: What is the total force? ii. Question # 5: Who won?

Click Return c. Using only the (blue) tallest person and one small person on the left

i. Question # 6: Without using the tallest red person, what combination of red persons do you need to have a sum of forces equal to zero?

Newton’s Laws of Force and Motion

3. Motion In this activity we study Motion because of force.

Return to the Main Screen and click on Motion

You should see

4. Setup a. Make sure the following boxes are checked (upper right in lab)

i. Forces ii. Values iii. Masses iv. Speed

b. Play with the lab to get familiar with the controls, specifically the play buttons for the Applied Force and see what happens going to the right and to the left.

5. Exercises:

a. Question # 7: Is there friction between the rails and the wheels of the cart? Explain your answer.

Click Reset (the orange round button on the right under the yellow box -- you will have to check the boxes in the yellow box again.)

Newton’s Laws of Force and Motion

Click the pause button (the left button under the yellow box) so you see the play button (||). Add two 50 kg boxes on the cart to make a total 100 kg Set the Applied Force to 100 N. b. Using your watch or any other time piece with a second hand (preferably a stopwatch,

which a smart phone will have), press Play and note the time (where the second hand is). i. Question # 8: How long did it take to reach 40 m/s from the time you clicked play

(round your answer to seconds)? ii. Question # 9: What is the acceleration? iii. Question #10: How far did the rail cart travel?

Click Reset and Pause (||) Add the two 50 kg box and the 200 kg box refrigerator to the rail cart. Again, set the Applied Force to 100 N.

c. Click Play and again note the time (to the nearest second) to reach 40 m/s. i. Question #11: How long in seconds to reach 40 m/s? ii. Question #12: What is the acceleration? iii. Question #13: What is the distance traveled? iv. Question #14: Compared to what was done in (h) above, why despite more

weight, did the rail cart travel farther?

Click Reset and Pause (||) Put the same 200 kg mass on the rail cart and set the Applied Force to 100 N.

d. Click play and stop after 40 seconds (by clicking on Pause)

i. Question #15: What is the final speed? ii. Question #16: What is the acceleration? iii. Question #17: What is the distanced covered? iv. Question #18: Does you distance answer make sense compared to the

distance found in (h) above? Explain.