For instance, the direction of the force of gravity on a freely falling body dropped from rest points towards the center of the Earth which is also the direction of displacement while falling. Hence, the force of gravity is said to be do positive work on the falling body. The falling body also experiences a upwards drag force due to air resistance.
Since the the drag force is being applied in the direction opposite to that of the motion, it's said to be doing negative work on the body. Sign up to join this community. The best answers are voted up and rise to the top.
Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Conceptually, what is negative work? Ask Question. Asked 8 years, 5 months ago. Active 3 years, 10 months ago. Viewed 96k times. Improve this question. Brandon Enright Negative work removes or dissipates energy from the system. Two examples : In pulling a box of books along a rough floor at constant velocity, I do positive work on the box, that is I put energy into the system.
Remember that Force is Mass times Acceleration. If Acceleration is negative such as when braking , then Force is negative. If the direction of motion and F are opposite, then negative work is being done. This means that energy is transferred in the opposite direction. For example, if you try to push a car uphill by applying a force up the slope and instead the car rolls down the hill you are doing negative work on the car. Can work be a negative value?
In the context of classical mechanics as you describe, negative work is performed by a force on an object roughly whenever the motion of the object is in the opposite direction as the force. Such a negative work indicates that the force is tending to slow the object down i. Is there a negative force?
It can negative. If the object is accelerating, then the situation is different. Can Net Force be negative? Forces can be positive or negative. Actually, forces which are aimed to the right are usually called positive forces. And forces which are aimed to the left are usually said to be in a negative direction. Notice that the net force is aimed to the left; so, it is a negative force. Why is work done by a conservative force negative?
Gravity is doing work on the object by pulling it towards the Earth, but since you are pushing it in the other direction, the work you do on the box and therefore the force is negative.
Is work a scalar or vector? Work is a scalar because it is the "dot" product of 2 vectors, also called the scalar product. Click the buttons to view answers.
The force is to the right and the displacement is to the right. F and d are in the same direction. Thus, positive work is done. The applied force of the racket causes the ball to gain speed.
Thus, the external or nonconservative force alters the kinetic energy of the ball. The force is up and to the right and the displacement is up and to the right. The applied force of the bat causes the ball to gain both height and speed.
Since the force has an up component, it contributes to a height change. Thus, the external or nonconservative force alters the both the kinetic energy and the potential energy of the ball. The force is to the left and the displacement is to the left.
The applied force of the hammer causes the nail to gain speed. Thus, the external or nonconservative force alters the kinetic energy of the nail. The force is to the left and the displacement is to the right. F and d are in the opposite direction. Thus, negative work is done. The friction force on the car causes the car to lose speed.
Thus, the external or nonconservative force alters the kinetic energy of the car. The applied force of the starting blocks causes the diver to gain speed. Thus, the external force alters the kinetic energy of the diver. NOTE: there is another force - gravity - which changes the diver's height; but the blocks are not responsible for this height change. The force is up and the displacement is up.
The applied force of the causes the barbell to gain height. Thus, the external or nonconservative force alters the potential energy of the barbell. Note that in the five situations described above, a horizontal force can never change the potential energy of an object. Horizontal forces cannot cause vertical displacements. The only means by which an external or nonconservative force can contribute to a potential energy change is if the force has a vertical component.
Potential energy changes are the result of height changes and only a force with a vertical component can cause a height change. Physics Tutorial. My Cart Subscription Selection. Student Extras. External Forces. Internal vs. F grav F spring. Fapp Ffrict. See Answer PE to KE The skier is losing height the final location is lower than the starting location and gaining speed the skier is faster at B than at A.
Kinetic energy.
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