Is there any situation in which friction can increase the kinetic energy of a moving object?

Question

Re: the baseball idea:

Yes, the overall speed of the ball would increase, but wouldn't the loss of rotational kinetic energy counteract the gain of translational kinetic energy? The ball would be travelling faster but with less rotation, with an overall loss of kinetic energy.

Answer 1

Nope.

In general, friction uses up potential energy by creating unusable heat. So when converting potential energy (PE) into kinetic energy (KE), we have PE - FE = KE; where FE is the friction energy lost. Thus, for a given PE, you can see that kinetic energy when FE > 0 is less than when FE = 0 and there is no friction

That answers your question. If you'd like more details, read on.

Note that FE = work = Fd; where F = friction force = kN, and k = coefficient of sliding friction (if the block is moving) or static friction (if it is not) and d = distance the block slides along the ramp (which is d = 0 if the block is not moving). N = normal weight of the block pushing onto the ramp = W cos(theta); where W = mg and m is the mass of the block, g is the acceleration due to gravity, and theta is the angle of the ramp's slope. Work is another name for expended mechanical energy.

In the block sliding down a ramp physics problem,

PE = mgh

FE = kNd = k W cos(theta) d = kmg cos(theta) h/sin(theta) = kmgh(cot(theta)), and

KE = 1/2 mv^2

Thus, from PE - FE = KE = mgh - kmgh(cot(theta)) = 1/2 mv^2

Notice that m, the block mass, cancels out on both sides of the equation. Thus we find 2gh(1 - k cot(theta)) = v^2 That is, the velocity (v) at the bottom of the ramp does not depend on the mass of the block.

The variables in 2gh(1 - k cot(theta)) = v^2 are:

h = height of the block at the beginning of its slide down the ramp
g = 9.81 m/sec^2 or 32.2 ft/sec^2 depending on units used
k = coefficient of sliding friction
theta = the angle of the slope in degrees
v = velocity of the sliding block when it reaches the bottom of the ramp

PS: Beware of false prophets. Those who believe friction increases the KE of a spinning baseball are not well informed. What friction does in that case is allow the angular energy of the spinning ball to convert to linear KE. But the actual friction energy (the work) is lost to heat mostly. That is, friction provides the traction or purchase that allows the angular energy to convert. But friction does not add energy of its own.

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Answer 2

Nope. It is impossible for friction to increase energy. Frictional forces cause energy loss. Friction is the opposing force that is trying to maintain equilibrium. Like if you roll a ball across the ground why did it stop. It stopped because there was a force working against the force of which you initially rolled the ball.

PROOF BY LAW AND THEORY

"According to the law of conservation of energy, no energy is destroyed due to friction, though it may be lost to the system of concern. Energy is transformed from other forms into heat. A sliding hockey puck comes to rest due to friction as its kinetic energy changes into heat. Since heat quickly dissipates, many early philosophers, including Aristotle, wrongly concluded that moving objects lose energy without a driving force."

Therefore according to the law of conservation of energy the energy is transformed into heat which is friction. The energy goes out of the object and is turned into friction

Newtons 3rd Law of motion

Newtons laws even tell us that there will be an opposing force!!!

"Whenever A exerts a force on B, B simultaneously exerts a force on A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line."

To simply put it.....for every action there is an equal and opposite reaction.

PROOF BY MATHEMATICS AND COMMON LOGIC

Energy is described as the ability to do work.
Work = F x r
F = force
r = displacement.

*Therefore energy is proportional to work;
work is proportional to force;
force is proportional to friction.

If friction decreases the force;
force decreases work;
work decreases energy.

The smaller the ability to do work the smaller the energy. Friction opposes all of these things.

In conclusion no there isn't any situation where friction can increases kinetic energy. That's like saying when you roll a ball across the floor that the ball is going to keep accelerating rather than slow down. That would be like saying when you drop a bouncy ball with each fall it gets higher and higher. We all know from observation that the ball gets closer to the ground with each bounce because of friction and the energy transfer after the collision.

Answer 3

im intrigued by ability of what the respond is... in step with risk it rather is a few thing like in case you're making use of a vehicle and the wheels are spinning the kinetic ability is low, yet while there become greater friction and the tires had greater effective purchase on the line floor kinetic ability would strengthen, so i'd wager, from a table sure place greater friction can enable for greater effective flow... (wager)

Answer 4

Yes. Imagine a fast moving baseball that also has top spin. The ball has kinetic energy of motion plus rotational energy. When the ball hits the ground, the friction causes some of the rotational energy to be added to the kinetic energy. The baseball actually ends up with a faster speed than what it started with.

Answer 5

yes, a simple example would be a baseball pitching machine

Answer 6

Most probably not.