A push can change a cart’s speed. The same push changes a light cart’s speed more quickly than a heavy cart’s. A stronger push can make the heavy cart gain speed faster. This change in speed each second is acceleration. Divide the net push by the cart mass to calculate it. The simple ratio applies to the resultant external force on a constant-mass object. Real carts can experience friction, changing forces and rotation, which this activity deliberately omits. Read the numerical acceleration as the model result; marker travel on the responsive drawing is a visual aid rather than an unlabelled physical length.
Forces, motion and energy · Discover & try
How do force and mass change acceleration?
Reading level 5 of 5 · AdvancedChange
Word help
Newton
The force unit that accelerates one kilogram at one metre per second squared.
Mass
A measure of resistance to acceleration.
Net force
The directional sum of external forces.
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See how it works
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Calculated constant-force motion from rest, with friction and rotation omitted.
What to look for
- It gains 2 m/s of speed each second.
- It gains only 1 m/s each second; the push has not changed.
- The heavier cart now gains speed as quickly as the first light cart.
Explain what you noticed
A separate 3 kg cart experiences a constant net force of 9 N. What is its acceleration?
Keep this idea: For a fixed mass, acceleration follows net force; for a fixed net force, more mass means less acceleration.
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