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# Question on pressure PHYSICS Watch

1. Suppose you have a ball attached to a string resting on the floor.

Force a; force of floor on ball= 2
Tension = 2
Weight =4

Area of ball in contact with floor is 0.5

Find the Pressure?
Will there be three values of pressure depending on which force u use ?

2. (Original post by ali malikzade)
Suppose you have a ball attached to a string resting on the floor.

Force a; force of floor on ball= 2
Tension = 2
Weight =4

Area of ball in contact with floor is 0.5

Find the Pressure?
Will there be three values of pressure depending on which force u use ?

You would have to calculate the pressure from the force in between the ball and the floor, which, in this case, is '2'.
3. (Original post by EricPiphany)
You would have to calculate the pressure from the force in between the ball and the floor, which, in this case, is '2'.
Thanks for the reply I really appreciate it. So in all cases would the force need to be the normal reaction force?
4. (Original post by ali malikzade)
Thanks for the reply I really appreciate it. So in all cases would the force need to be the normal reaction force?
If you are asked for the pressure in between the ball and the floor, then yes.
Atoms will be squashed together under the ball, providing the normal force, and the atoms in the string will be stretched apart (very slightly).
5. (Original post by ali malikzade)
Thanks for the reply I really appreciate it. So in all cases would the force need to be the normal reaction force?
and remember to divide by the area of contact
6. (Original post by EricPiphany)
If you are asked for the pressure in between the ball and the floor, then yes.
Atoms will be squashed together under the ball, providing the normal force, and the atoms in the string will be stretched apart (very slightly).
Thanks a lot man one last question. Why couldn't it be weight used ?
7. (Original post by ali malikzade)
Thanks a lot man one last question. Why couldn't it be weight used ?
Imagine the string supplied a force equal to the weight of the ball. Would you still use the weight to calculate pressure? (there would be no pressure at all)

Part of the weight is cancelled by the tension in the spring. Less force from the floor is needed to keep the ball in equilibrium.

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