When they do not balance
A trolley is pushed, and then the push stops. Does it keep speeding up?
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Step 1 of 3
- A push acts. The trolley speeds up.
- The push stops. If nothing else acts, the speed holds.
- A push the other way acts. The trolley slows down.
The rule
No. It speeds up only while a net force acts.
Forces are unbalanced when a net force is left over. The net force changes the motion. A net force can speed up, slow down or turn an object. To turn is to change direction.
A change in speed or direction needs a net force.
Watch out!
A real trolley slows after the push ends. Friction is a force that acts against its motion.