You stand in a city bus without holding the rail…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
You stand in a city bus without holding the rail.
- The driver brakes suddenly. Which way does your body tend to fall, and why?
- Later, the bus starts quickly from a stop. Which way do you tend to fall?
- Your friend says: 'When the bus brakes, a force throws you forward.' Is that right?
Need a reminder? The key ideaShow
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) Forward. The floor slows your feet, but the rest of your body keeps moving forward by its inertia.
Step 2. (b) Backward. The floor carries your feet forward while your body tends to stay at rest.
Step 3. (c) No. Nothing throws you forward; your body simply keeps moving while the bus slows under you.
Answer: Forward, then backward; no forward force acts, it is inertia.
Check. That is why we hold the rail: it gives the unbalanced force that changes our motion with the bus's.
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