Understanding Work and Friction: Exploring Direction and Energy in Motion

In summary, when calculating work involving friction, it is important to consider the direction of the net force and displacement. If friction is present, the total work done is equal to the change in kinetic energy plus the work done against friction. However, if there is no friction, the total work done is simply equal to the change in kinetic energy. It is important to accurately determine the direction of the net force and displacement in order to properly use the work formula.
  • #1
jongro
4
0
Since friction is in the opposite direction as the direction of movement, wouldn't you expect the work to be negative? When I put it in the work formula, W = F * cos(180O) * d
it comes out positive because F is negative and cos(180) is negative too.

This means that if I have another force pulling something across a surface, then it would do more work if there is friction.

I read somewhere that the work is equal to the change in kinetic energy between two points but I was working on some homework and I realized that the only way I could get the right answer is if I made is so that W = F * cos(0O) * d (instead of theta = 180) in the friction work formula; that way friction gives negative work and when I add the two it equals to the change of kinetic friction.

Is there anything wrong in my original reasoning that W = F * cos(180O) * d?
I'm generally confused about work, could someone explain to me how it works?
 
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  • #2
in a case of no friction

total work done= change in kinetic energy


with friction

total work done= change in kinetic energy + work done against friction

or if you want

total work done= change in kinetic energy - work done by frictional force
 
  • #3
If the kinetic energy of the body increases, the work is done on the body. If the kinetic energy decreases, the work is done by the body.
So you have to decide the direction of the net force and the displacement before using the formula.
 

1. What is work and how is it calculated?

Work is defined as the measure of the force applied over a certain distance. It is calculated by multiplying the force applied by the distance moved in the direction of the force.

2. How does friction affect the movement of objects?

Friction is a force that resists the movement of objects. It acts in the opposite direction of the object's motion and can slow down or stop the object's movement.

3. What are the three types of friction?

The three types of friction are static friction, kinetic friction, and rolling friction. Static friction occurs when two surfaces are not moving relative to each other. Kinetic friction occurs when two surfaces are moving relative to each other. Rolling friction occurs when an object rolls over a surface.

4. How can friction be reduced?

Friction can be reduced by using lubricants, such as oil or grease, between two surfaces. Another way to reduce friction is by using smoother surfaces or by applying less force.

5. What is the difference between speed and velocity?

Speed is the measure of how fast an object is moving. Velocity is the measure of how fast an object is moving in a specific direction. Speed is a scalar quantity, while velocity is a vector quantity.

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