In mos situations the friction force reduce the kinetic energy however frictional force can sometime increase the kinetic energy describe a few situations in which friction causes an increase in kinetic energy
Answers
Explanation:
The torque of a force
→
F
about an axis is given by the equation;
→
τ
=
→
r
×
→
F
where,
→
r
is the position vector of the point where the force is applied from the axis of rotation.
Answer and Explanation:
In general, the frictional force acts as an opposing force and thereby affects the kinetic energy of the body by diminishing its speed. However, the...
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Friction is a force. Its direction is that it tries to equalize the velocity of two objects.
Kinetic energy is actually relative. It depends what reference frame you’re looking in to determine whether friction is increasing or decreasing the kinetic energy. For example, if we look at the reference frame of one of the objects, the kinetic energy of the object will decrease (if we’re talking about kinetic friction, if it’s static, the two objects are already have 0 kinetic energy in each other’s reference frames).
A case like walking or driving a car is slightly more complicated. The reason for this is that we have static friction and relative motion in the ‘object’. The kinetic energy of your foot against the ground is 0. The kinetic energy in your body comes from pushing off your foot, which doesn’t just slide because of static friction.
But we can imagine a case where kinetic friction would directly increase kinetic energy in, say, the rotating reference frame of Earth’s surface (or just look at the local area of the Earth’s surface which is instantaneously moving linear).
For example, you know those conveyor belts at cashiers in some stores (at least in US)? When you set an object on it without moving it with the belt with your hand first, kinetic friction accelerates it up to the speed of the belt, increasing its kinetic energy in Earth’s reference frame (in the belts, for example, it decreases, and in the object’s own, it doesn’t change because it’s always 0).
P.S. Anyone bothered by the fact that energy is conserved but kinetic energy changes when you change reference frames (I was), I suggest working out the following problem:
Imagine you have a stationary (in your reference frame) ramp (tethered to the Earth or whatever so it has ‘infinite’ mass) and on the top you have a ball. The ball starts with some potential energy ( EE ) and it rolls down and gets converted to kinetic energy and it has some velocity vv .
Now imagine the same situation, except the ramp and ball both start moving at vv . Initially, it feels like in the second case, energy is not conserved. The ball has initial energy of EE in potential energy and EE again in kinetic energy, so 2E2E , but at the end, it is moving at velocity 2v2v , corresponding to 4E4E kinetic energy. Where did the extra 2E2E come from?
Imagine the ramp having finite mass, figure out what happens, and then take the limit as the mass of the ramp approaches infinity and you get your answer.
Hope it's helps you
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