Forces and Motion


· To understand the relationship between applied force, net force, acceleration, and mass for one-dimensional motion.

· To understand how the forces exerted on an object on an inclined plane affect the object’s motion.

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Use the PhET simulation Forces and Motion: Basics.


This simulation allows you to push on different objects with a certain horizontal force and see the resulting motion. You can control the mass of the object by using different objects or by stacking up to three objects on top of one another. Click and drag on the objects to move them to the desired location. You can also adjust Friction between None and Lots by using the slider provided on the right side of the window.


While the object is being pushed, you can see the directions and values of the various horizontal forces acting on it, as well as the value of the sum of these forces. In addition, you can display the mass, speed, and acceleration of the object.



1. Open up PHET simulation Forces and Motion: Basics

2. Click “Net Force”

3. Place 2 people that are the same size the same distance away from the cart.

4. Make a prediction about the movement of the cart.

5. AFTER you have observed the actual movement, click on the sum of the forces box at the top right-hand corner of the simulation. Record the number in the data table.

Tasks Predicted Movement


Actual Movement

(none, left, right)

Sum of Forces

(0, x-left, x-right)

Same size, same placement on rope.


Same size, different placement on rope.


Different size, same placement on rope.


Different size, different placement on rope.



Fill in the following table with the values of the forces (some boxes have more than one possible correct answer). Capture and insert the screenshot when completing the last three rows.

Situation Force to the right (N) Force to the left (N) Net force

(N, left or right)




100 N 200 N
150 N, right
100 N, left


Question-1: What causes objects to move or stay still?



Question-2: Balanced forces cause a change in motion. True or false? How do you know this?

Question-3: Unbalanced forces cause a change in motion. True or false? How do you know this?

Question-4: What do you think would be the best way to divide up your friends for the game of tug-of-war? Be sure to explain your reasoning.