Question

can frictional forces ever increase an object's kinetic energy?

Answer 1

Like a tire on a road i guess is considered positive work

Answer 2

Welcome to openstudy!
As you know frictional force is always opposite of the motion. Imagine a car moving on the road and the friction is the ground on the tires of the car.

Frictional forces cannot increase an object's kinetic energy. Kinetic energy is considered positive because the motion is positive. If my explanation was helpful. Give me a medal and feel free to ask more questions to clarify it much more for you. :)

Answer 3

@korosh23 Frictional forces do in fact increase kinetic energy. The car driving down the road is able to move because of the friction. It is true that the force is opposite of motion, but that is not the question. Can friction force increase the objects kinetic engery, and the answer is Yes.

Answer 4

@Austin6i6 you are right about that the friction force lets objects move. I completely agree with that. Kinetic energy occurs in any object which has motion and speed in it. If you look at the question again, you can realize it does affect the kinetic energy.

Answer 5

Friction reduces kinetic energy force. The answewr is no it cannot increase the objects kinetic energy.

Answer 6

I have found multiple source that say my answer is correct. Would you like me to list Some?
@korosh23

Answer 7

Ok, but tell me why my answer is incorrect? I might be making a mistake,

Answer 8

i see your logic, And i originally said no as well. The mistake is that your accounting for direction. We are talking pure magnitude. The friction in the car is increasing the kinetic engery. Kinetic energy is not a vector it is a scalar.

Answer 9

its almost like a trick question in a sense

Answer 10

Ok you are right about the direction of the kinetic energy. How do you know the person meant pure magnitude?

Answer 11

because kinetic energy does not have a direction

Answer 12

http://www.physicsclassroom.com/class/energy/Lesson-1/Kinetic-Energy
@korosh23

Answer 13

Ok you are right! If the person was thinking about pure magnitude. He would choose your explanation If not he would choose mine. It is a win- win situation! We both explained.

Answer 14

But kinetic energy is always pure magnitude Never ever ever ever ever has a direction lol
:)

Answer 15

your logic was good though

Answer 16

A friction force can increase kinetic energy. (Unfortunately, the car tire is the wrong example)
But in order to do so, the base acting on the body must be in motion:
- a conveyor belt will increase the KE of the object standing on it
- pulling a piece of paper with a block resting on it will increase the block's KE.

In the case of the car tire, the road's friction on the wheel acts forward, but the power provided is either zero (if no slipping occurs) or negative (if slipping occurs).
The car's increase in KE is provided by internal actions, such as the engine's torque on the wheels.

This is one of the truly non-intuitive prolems with friction:
When the base is fixed, friction can provide acceleration, but it cannot provide KE.