Hi guys,(eagle i cleared up about FBD n can help me clarify if im rite here? thanks)
1) when an object is at rest on the ground/table forces acting on the object or Free body diagram is: Weight and contact force of earth/table acting on the object. both are acting on the object itself
Free body diagram of the earth/table: contact force of object on table/earth gravitational pull acting on the earth/table. both forces are opposite from each other and both acting on the earth only
so my question here is whether the reason i feel a book as heavy is because of the contact force acting on my hand by the book? and not weight? Thanks
2) (link to question 1)when an object is on a pivot plank thing, and they say the object weights 500N. then immediately we would label a force 500N downwards by the object rite? but is that 500N really weight or is it contact force on the plank by the object? (similar to my first question)
3) (link to question 2) so if im rite about the contact force being the force acting downwards, then does it mean that the contact force on the object by the plank is NOT equal to weight at first and so it falls down. until it hits a solid and not moving object then the contact force increase to the same magnitude as the weight? while looking at the Free body diagram of the plank, the contact force is more than the gravitational pull of the plank by the object and so the plank moves downwards. only when it hits the ground then the contact force decreases the the same magnitude of the weight?
thanks for answering my question btw when answering can u put a 1) 2) 3) for each of the question so that ill be able to locate and thus better understand it better? thanks
[1] Contact force on hand: F = m x a
In this case, the book's mass is the m and when you multiply by gravity, a, you get F which is the weight. Mass =/= weight and weight = force.
[2] Again, weight = acting force. At around 9.81 m^2/s, the F=500N gives you object mass of ~51 kg.
[3] I don't understand what you're trying to say but again, F = m x a and I think you're confusing mass and weight concept?
Oh and moment = Force x distance from pivot point.