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InvalidID
- 84
- 3
If a force is applied to a box, and the box is not displaced, no work is done on the box, right? But to apply the force, don't you use up calories which is a unit of energy?
Khashishi said:Your body wastes energy, but it doesn't accomplish any work on the box. This is because your body is inefficient in metabolizing food and generating forces.
Drakkith said:No. Consider gravity. Gravity acts upon a box sitting on the ground, applying a force that pulls it down. If we watch the box we will see that it does not move, there is no displacement. As such there is no work done on it. Also, no energy is expended by applying this force.
Now, this changes a little bit if you talk about using machines, such as your body, to apply a force. Your body is not a perfect machine and must expend energy to apply any force using its muscles. In such a case you would indeed use up calories, but this energy is used up in your body, and the work performed is on your body, not on the box.
InvalidID said:So where does the energy go?
InvalidID said:I'm still having trouble with work & energy.
Consider a ball that starts 1m above the ground and falls down to the ground without bouncing. All of the ball's gravitational energy is converted into kinetic energy, right? But we also know that work was done on the ball. So if all the energy is converted from gravitational energy to kinetic energy and there is no energy left to do work, then how has work been done?
InvalidID said:I'm still having trouble with work & energy.
Consider a ball that starts 1m above the ground and falls down to the ground without bouncing. All of the ball's gravitational energy is converted into kinetic energy, right? But we also know that work was done on the ball. So if all the energy is converted from gravitational energy to kinetic energy and there is no energy left to do work, then how has work been done?
InvalidID said:Is work the only process that energy can be transferred through? If so, then whenever energy is transferred, there will always be a force and displacement involved?
According to the laws of physics, an object will only move if there is a net force acting on it. If the force applied to the box is equal and opposite to the friction force, the box will not move and no work will be done.
In physics, work is defined as the product of force and displacement. If there is no displacement, then no work is done.
Work is the energy transferred to an object when a force is applied and it causes the object to move. Displacement is the distance and direction of the object's movement. In order for work to be done, there must be a displacement in the direction of the force.
Besides force and displacement, the angle between the force and displacement vectors also affects the work done on an object. If the force and displacement are perpendicular, then no work is done.
Imagine a person holding a weight in their hand. As they walk, they are exerting a force on the weight but it is not moving. Therefore, no work is being done on the weight. Only when they lift the weight or move it horizontally, work is being done on the weight.