Why is no work done by the force of gravity when a body moves in a horizontal surface?

Answer 1

Because work is defined as a force acting upon an object to cause a displacement. Since the force (gravity), acting on the object doesn't cause a displacement (the object didn't move vertically, only horizontally), no work occured.

Here's a page that explains it in detail (which I found after searching google for 30 seconds).

Answer 2

No gravity = No friction = A very minute force to move the body.

Where friction is present it will have to be overcome by a greater force in the horizontal direction.

By applying just sufficient force to move the body then by drawing to scale the downward force (mg) and the force to move the body a right angled triangle of equilibrium will enable the friction angle to be calculated.

In short NO WORK is done by gravity but the actual work done depends upon the frictional resistance to movement which depends upon the nature of the two surfaces in contact.

Skating on ice is easier (small force) than skating on a rubber mat (greater force)!

Downward force F would still = mg in both cases.

Answer 3

It is possible that the problem you are working on has simplified this part of the problem out, but generally the force of gravity would have an effect modified by the coefficient of friction between the moving body and the surface, which would result in an acceleration in the direction opposite the body's movement.

Answer 4

Work can only be done when something changes. Because gravity is acting downwards and the body does not move in that direction no work is done. If there was no gravity the body wouldn't just float away it would remain on the surface.

Answer 5

Work is a scalar quantity i.e. it has only magnitude. It is equal to force multiplied by displacement. The product is = F a cos(theta). Gravity acts downwards or in the vertical and displacement in horizontal direction m so the angle between the two is 90 deg . Cos (90) = 0 . Therefore work done is zero.

Answer 6

Newtons third law of motion. To every action (force applied) there is an equal and opposite reaction (or force)
The gravity is exerting a force on the object, but their is an equal and opposite force pushing up from the surface of the ground onto the object, giving a net result of zero for force in the vertical plane.

Answer 7

err.... it is. but the overiding force is one that sends it along a horizontal plane. I'm assuming you mean if it is on a table or something. Gravity does not have enough force to pull it through the surface so it can olny move sideways. If it runs out if surface it will fall.

If it is a projected object like a trown ball or a bullet, gravity will bring it down to the nearest surface the object cannot pass through.

Answer 8

It is, all actions have an opposite and equal reaction.

Gravity is trying to push the object through the surface, however the molecular force between the object and the surface is counteracting the force of gravity.

Answer 9

Horizontal motion and vertical motion are independant. Gravity therefore doesn't affect the horizontal motion. Imagine a bullet being fired parallel to the earth from a gun 1 metre above ground, and at the same time dropping a bullet from the same height. They will hit the ground at the same time.

Answer 10

But surely gravity is keeping the body on the horizonatal surface? Also the body is not moving vertically, hence why gravity does not come into the forces at work, it is kinetic energy that moves the body.