Say whether the forces on each object are balanced or unbalanced, and give a reason…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Say whether the forces on each object are balanced or unbalanced, and give a reason.
- A pen lies on a desk.
- A bus pulls away from a stop.
- A cyclist rides at a steady on a straight, level road.
- A ball thrown straight up is at the top of its path, at rest for an instant.
- A car goes round a bend at a steady speed.
Need a reminder? The key ideaShow
The net force adds all the forces with their directions. If it is zero the forces are balanced and the motion does not change; if not, they are unbalanced and the object speeds up, slows down or turns. Forces at right angles are added separately.
Newton's first law: an object stays at rest, or keeps moving in a straight line at a steady speed, unless an unbalanced force acts on it. Inertia is this tendency to keep the same motion; more mass means more inertia.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Balanced: it stays at rest.
Step 2. (b) Unbalanced: it speeds up.
Step 3. (c) Balanced: steady speed in a straight line.
Step 4. (d) Unbalanced: gravity still acts and the ball starts falling at once.
Step 5. (e) Unbalanced: the direction changes, so the velocity changes.
Answer: Balanced: (a), (c). Unbalanced: (b), (d), (e).
Watch out. 'At rest for an instant' is not the same as balanced.
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