Physics can you have negative work

If so, will these models allow learners to more completely address the complexity of energy processes, both those involving the human body and those which do not. Sue lives at the 15th floor of an office building. She like to get exercise by climbing the stairs to her office rather than taking the elevator. The building is air conditioned and always kept at a constant temperature of 72 F. She always walks up the stairs and down the stairs in the same amount of time.

Sue notices that she consistently perspires more on the way up the stairs then she does on the way down. What do you think is different about the energy transfers and transformations that Sue experiences on her way up and down the stairs? How can you account for the observation that she perspires more on the way up the stairs?

Most of me stayed at the same gravitational potential. I did have to lift my legs more than on a flat treadmill but that, near as I can tell, was the only additional work I had to do.

Not nearly as much work as climbing a hill. Is it possible to engineer a treadmill to light a light bulb with no external energy source other than the person running on the treadmill?

If so, should the treadmill be inclined, declined or horizontal? We can also say that work done by a force is negative if the applied force has a component in a direction opposite to the displacement.

Similarly, frictional force is always opposing the relative motion of the body. When a body is dragged along a rough surface, the frictional force will be acting in the direction opposite to the displacement. The angle between the frictional force and the displacement of the body will be o.

Thus, the work done by the frictional force will be negative. Toggle navigation Tutor 4 Physics. It was mentioned earlier that the waiter does not do work upon the tray as he carries it across the room.

The force supplied by the waiter on the tray is an upward force and the displacement of the tray is a horizontal displacement. As such, the angle between the force and the displacement is 90 degrees. If the work done by the waiter on the tray were to be calculated, then the results would be 0. A vertical force can never cause a horizontal displacement; thus, a vertical force does not do work on a horizontally displaced object!! It can be accurately noted that the waiter's hand did push forward on the tray for a brief period of time to accelerate it from rest to a final walking speed.

But once up to speed , the tray will stay in its straight-line motion at a constant speed without a forward force. And if the only force exerted upon the tray during the constant speed stage of its motion is upward, then no work is done upon the tray. Again, a vertical force does not do work on a horizontally displaced object.

The equation for work lists three variables - each variable is associated with one of the three key words mentioned in the definition of work force, displacement, and cause. The angle theta in the equation is associated with the amount of force that causes a displacement. As mentioned in a previous unit , when a force is exerted on an object at an angle to the horizontal, only a part of the force contributes to or causes a horizontal displacement. Let's consider the force of a chain pulling upwards and rightwards upon Fido in order to drag Fido to the right.

It is only the horizontal component of the tension force in the chain that causes Fido to be displaced to the right. The horizontal component is found by multiplying the force F by the cosine of the angle between F and d.

In this sense, the cosine theta in the work equation relates to the cause factor - it selects the portion of the force that actually causes a displacement. When determining the measure of the angle in the work equation, it is important to recognize that the angle has a precise definition - it is the angle between the force and the displacement vector. Be sure to avoid mindlessly using any 'ole angle in the equation.

A common physics lab involves applying a force to displace a cart up a ramp to the top of a chair or box. A force is applied to a cart to displace it up the incline at constant speed.

Several incline angles are typically used; yet, the force is always applied parallel to the incline. The displacement of the cart is also parallel to the incline. Since F and d are in the same direction, the angle theta in the work equation is 0 degrees. Nevertheless, most students experienced the strong temptation to measure the angle of incline and use it in the equation. Don't forget: the angle in the equation is not just any 'ole angle.

It is defined as the angle between the force and the displacement vector. On occasion, a force acts upon a moving object to hinder a displacement. Examples might include a car skidding to a stop on a roadway surface or a baseball runner sliding to a stop on the infield dirt. In such instances, the force acts in the direction opposite the objects motion in order to slow it down.

The force doesn't cause the displacement but rather hinders it.