You are riding on the bus on the way to school. the bus is motionless. when the bus starts to move you are forced toward the back of the bus. Which of the 3 of Newton's Laws applies here?
Newton's third law: For every action there is an equal and opposite reaction.
actually stormfires reply isn't really correct... it is more of the first law "Anything that is moving will keep moving at the same speed and in the same direction unless a force changes it." therefore when the bus moves you are forced into your seat as your body is trying to stay at a standstill due to the laws of inertia.
I believe the third law still applies here because there are action/reaction pairs. However, I can see where the first law is the better answer.
stormfire1 - There is no pair of forces here. You are not being forced to the back of the bus by any force...this is just you having a noninertial reference frame (that of the inside of the accelerating bus). It only looks like you are being accelerated backwards because the bus is moving forwards around you.
In theory ,when you take earth as the frame of reference, the bus as well as you standing in it would accelerate in the direction of the net force(i.e. the direction of motion of the bus). But when you take the bus as the frame of reference you seem to be stationary. So if the bus is accelerating you need a force which has a magnitude equal to the product of your mass and the acceleration of the bus, in a direction opposite to the motion of the bus so as to keep you stationary in the frame of reference of the bus. And practically that is the force that pushes you backwards when the bus moves suddenly.
the answer as aceace pointed out is newton 1st law more specifically it can be pointed at the inertia of rest of the feet
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