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A puck that keeps gliding
Age 15 · Physics
An object keeps its state of motion, either at rest or moving in a straight line at constant speed, as long as the forces on it cancel out. A net force is what makes it speed up, slow down or change direction.
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Age 15: open this week
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In the picture
- Puck gliding on air: balanced forces, steady straight motion
- Evenly spaced ghost images: equal distances in equal times, so constant speed
- Bent path: the direction changes because a net force acts
- Magnet: the sideways pull that unbalances the forces
Examples
- A hockey puck sliding across smooth ice keeps going almost unchanged until a stick hits it.
- Passengers lurch forward when a bus brakes, because their bodies tend to keep moving at the same speed.
Key takeaways
- Balanced forces: no change in motion, whether at rest or moving at constant speed in a straight line.
- A net force changes speed, direction, or both.
Quiz: A puck that keeps gliding (Age 15)
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A puck glides in a straight line at constant speed. What does this tell you about the forces on it?
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What can a net force do to a moving object?
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An object covers equal distances in equal times. What does this show?
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