Newton's First Law

[chaput]

Hi there,
I usually get stuck with the questions that are to do with explaining of the Newton's Law's and I have no idea where to start and how to relate to inertia. Inertia is a really confusing topic for me:/ Could someone please help me out with this?

An example question is:
A student is travelling to school on a train. When the train starts moving, she notices that passengers tend to lurch towards the back of the train before grabbing a handrail to stop themselves from falling. Has a force acted to push the passengers backwards? Justify your answer.

Thank you!! Have a great term holiday:)

[MrSpacecan]

Basically, inertia is a property of objects with mass have which causes them to resist being accelerated - they like to remain at rest or at constant velocity. In the context of the example question, if the train were to start moving, they don't necessarily lurch backwards because there is a force acting upon them, rather that they are being accelerated from a state of rest into one which is moving, and because of Newton's first law, they will resist the sudden movement of the train; this will lead to them falling backwards. Hope this helps

Sorry, I forgot to mention that mass is a measure of an object's inertia - so, if you were to shove a person, you'd notice that they would move pretty easily - whereas if you were to try and shove a car, you'd notice that it does not move very much at all. So basically, the more mass, the more inertia (the more it will resist being accelerated).

Mod edit: merged double post

[Richard Feynman 101]

Ah, Inertia.

Really, what is inertia? We do not know, people here don't, teachers do not and even theortical physcisit do not. A simple definition is that inertia is the tendancy for objects to remain in motion. But what causes inetia? We do not know. Just like gravity; we do not know what it is, we can calculate it (VCE physics g = gm1m2/r^2 is just an estimate - in reality we use general relativity however this is beyond this website. Yeah, I wouldn't worry about 'what is inertia.' It is just means that objects tendancy to remain in motion (throw a ball it would theorytically, however, not practical due to conservation of enrgy travelling in a straight line forever, however, it is slowed down by air resistance highlighting Newton's first law of motions stating that objects will remain in a constant velocity unless acted upon an external force. In this case air resistence.

[Richard Feynman 101]

Basically, inertia is a property of objects with mass have which causes them to resist being accelerated - they like to remain at rest or at constant velocity. In the context of the example question, if the train were to start moving, they don't necessarily lurch backwards because there is a force acting upon them, rather that they are being accelerated from a state of rest into one which is moving, and because of Newton's first law, they will resist the sudden movement of the train; this will lead to them falling backwards. Hope this helps

Sorry, I forgot to mention that mass is a measure of an object's inertia - so, if you were to shove a person, you'd notice that they would move pretty easily - whereas if you were to try and shove a car, you'd notice that it does not move very much at all. So basically, the more mass, the more inertia (the more it will resist being accelerated).

Mod edit: merged double post

This is a very confusing topic to grasp and can be hard to understand. But what you have said is actually wrong. Think about this you have a pull-cart and a tennis ball in it. Look at the car and ball horizontally and accelrate it foward. You'll notice that the ball rolls back only slightly. Okay, this can be confusing but it is due to the friction. Therefore are two things that act on an object that is, static friction (unchanging) and also kinetic friction (yes, this is beyond the course, however, mistakes will be previtably! In order to over come the static friction - kinetic static energy is required and thus, it actually roles back a little bit. So it is the friction between the cart and the ball.