Calculate Acceleration from Net Force

Supplied materials

• Use the supplied fictional observations or model. Paper and pencil are optional; spoken answers are welcome. No equipment or real experiment is needed.

Learn the idea

Net force changes velocity through acceleration. For constant mass in this model, acceleration a = net force Fnet divided by mass m. Right is positive. A positive acceleration means the velocity changes toward the right; it does not prove that the cart is already moving right. List all horizontal forces before using the equation.

A fictional 2 kg cart has +10 N right and −4 N left, with no other horizontal forces; vertical forces balance. Its horizontal net is +6 N, giving a = 6/2 = +3 m/s². This means its right-positive velocity changes by +3 m/s each second while the forces stay constant. A second 4 kg cart with the same net force would have only +1.5 m/s² acceleration.

1. Add +10 and −4 N to obtain the horizontal net.
2. Divide by 2 kg and label the result m/s².
3. Compare with a 4 kg cart under the same net force.
4. State why starting velocity is separate information.

Check your reasoning

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Take it further

Change the left force to 15 N. Net force becomes −3 N, giving −1 m/s², or 1 m/s² left, for the same 3 kg mass.

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