In physics work is defined as Force X Displcament?

Question

If you have 10kg shopping bag in your hand and stuck in a bus queue standing still, you still get tired doing zero work according to physics. What is going on?

Answer 1

Your muscles repeatedly contract and relax which uses energy even though no work is done on the bag.

Answer 2

Okay, for any object to remain still it must all the forces on it balanced (newtons laws).

Now yets take a closer look at the bag...Weight is a force, mg (mass * gravity). So we now have a downward force acting on the bag. So inorder for the bag to be still we must be suppying a equal and opposite force.

This force can be calucated by F = mg = 10*10 = 100

well we are suppying a force to keep it still.

Also work is defined as force times the displacement.
(W = F.ds or this form might be more familar W=F*X)

Also on an another note, when you asked the question you asked it in terms or work. Now here something important to remember in physics, you have to be doing work to appied forces!

Answer 3

Force = m x g

= 10 x 9.81 = 98.1N
The bag is pulling down on the arm muscles or the arm muscles are pulling up with an equal force = a force of 98.1N ... the work done is the expenditure of energy - aching muscles.

Answer 4

You begin to realize that life is to short to wait for a bus