Friction and conservation of energy

• Keiran OConnor
In summary, the conservation of energy law does not allow energy to be lost, but friction causes conversion of mechanical energy to heat energy.

Keiran OConnor

How does friction lose energy when the conservation of energy law doesn't allow energy to be lost ??

Sorry if this is a stupid question I have tried googling but can't find much to help.

Keiran OConnor said:
How does friction lose energy when the conservation of energy law doesn't allow energy to be lost ??
Friction causes conversion of mechanical energy to heat energy.. The surfaces become warmer. There's no loss of energy.

Drakkith
+1

If you ever find an apparent breech of conservation of energy it invariably means you have drawn your system boundary in the wrong place (eg you have forgotten a means by which energy can enter or leave your system). In other words your system isn't "closed". Conservation of energy only applies to closed systems.

Keiran OConnor said:
friction lose energy when the conservation of energy law doesn't allow energy to be lost ??

The confusion is coming from looking at the problem from two different viewpoints. Consider a block of mass M sliding down a frictionless ramp from a height H. The block initially has potential energy ##E_p = MgH##. We know that at the bottom of the ramp all of that potential energy will have been transformed into kinetic energy ##E_k ## resulting in a velocity of ##v=\sqrt{2gH}## at the bottom of the ramp. So we say energy is conserved because the starting energy is equal to the ending energy, or ##E_p - E_k = 0##. So far so good?

Now consider that the ramp is not frictionless. In this case the velocity must be ##v<\sqrt{2gH}##. The reason we know that the velocity is less than the previous value is that we know energy is always conserved! Some of the energy of the block was transferred to the ramp due to friction in the amount ##E_f##. If we only consider the energy of the block it will seem like some energy disappeared somewhere along the way to the bottom of the ramp. But we know the energy did not disappear, it was both transformed and transferred in the friction case but only transformed in the non friction case. In the friction case we still have ##E_p - E_k - E_f = 0##, and so we see energy is conserved, as always.

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What is friction?

Friction is the force that opposes the motion of an object when it comes into contact with another object or surface. It is caused by the molecular interactions between the two surfaces.

How does friction affect the conservation of energy?

Friction converts some of the kinetic energy of an object in motion into heat energy. This means that the total amount of energy in a closed system is not conserved, as some of it is lost to friction.

Can friction ever be beneficial?

Yes, friction can be beneficial in some situations. For example, it allows us to walk without slipping, helps vehicles stop, and enables us to grip objects with our hands.

How does the type of surface affect friction?

The type of surface can greatly affect the amount of friction between two objects. Rough surfaces typically have more friction than smooth surfaces, and the type of material also plays a role. For example, rubber has more friction than ice.

What factors affect the amount of friction?

The amount of friction is affected by several factors, including the force pushing the two objects together, the type of surfaces, and the speed at which the objects are moving. Additionally, the presence of lubricants or other substances can also impact friction.