# Examples in which force is exerted on an object without doing work

1. Oct 10, 2004

### Faiza

Q.Give two examples in which force is exerted on an object without doing any work on the object.

ummm i cant think of any example, i think the upward force does not cause the horizontal displacement so this is a NON-example of work????

2. Oct 10, 2004

### Fredrik

Staff Emeritus
I'm sure you know how "work" is defined. If the force isn't zero, then something else has to be (in order to make the work zero). What is that other thing? If you understand that, I don't think you will find it difficult to think of two, or even two hundred, examples.

3. Oct 10, 2004

### Faiza

work is force and displacement in the same direction so

4. Oct 10, 2004

### Faiza

example

force of gravity?????????? cud that be one

5. Oct 10, 2004

### Faiza

Any time a force is exerted but the object is not displaced in a direction parallel to the force, work is not done.

Force of tension on a ball rotating on the end of a string.

Normal force and gravitational force on an object at rest or moving across a level floor.

6. Oct 10, 2004

### TenaliRaman

Faiza u r close but not close enough!

Work is defined as dot product of Force vector f and displacement vector s.
W = f.s = fscos(theta)
where theta is the angle between f and s.
if this theta is pi/2 then cos(pi/2)=0 hence W = 0

if f is perpendicular to s then W = 0.

-- AI

7. Oct 10, 2004

### Faiza

ohh okay........i get it

8. Oct 10, 2004

### Faiza

Thanksss!!!

9. Oct 10, 2004

### Faiza

any other examples?

10. Oct 11, 2004

### Fredrik

Staff Emeritus
Any force that doesn't move the object is a good example. Suppose e.g. that you're standing still on a slope. There are three forces acting on you, but none of them is doing any work, so you have three good examples right there.

11. Oct 11, 2004

### Spectre5

Go stand next to a solid wall and push on the wall as hard as you can....assuming the wall does not move...then you did no work on it.