# Is friction related to velocity?

1. Nov 26, 2015

### avito009

I was mixing sugar in a glass of lemonade. As i stirred the spoon I thought that if I move the spoon faster it would cause the lemonade to heat up and thus increasing the temperature. Will the spoon cause heat to be generated in the lemonade? Also answer the title question.

2. Nov 26, 2015

### Apoorv3012

Friction does not depend upon velocity of the object but the material of the surface(over which object is moving) and the object, also friction depends upon the normal force N acting on the object by the surface.
Also on a microscopic level friction is caused by electrostatic forces between the object and the surface.

Yes the temperature of te lemonade will rise up on continuous stirring, infact this was done by Boltzmann in his water churning experiment to obtain the relation between joules and calories. Where 1 Calorie = 4.186 Joules. This ultimately killed the myth of "calorific fluid" which was then used to explain transfer of heat.

3. Nov 26, 2015

### Staff: Mentor

The frictional force between two objects in not affected by their relative speed.
The amount of work done by that force (and hence the heat generated) is affected by their relative speed.

4. Nov 26, 2015

### avito009

Is it the force of friction between the spoon and water?And does this friction cause an increase in temperature?

5. Nov 26, 2015

### Staff: Mentor

Yes and yes.

6. Nov 26, 2015

### nasu

The resistance encountered by the spoon moving through water is not the same as the friction between solid surfaces. It does depend on the speed.
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7. Nov 26, 2015

### Apoorv3012

Those are viscous forces that cause the heat inside this type of system, viscosity is ànalogous to friction in such system with a working fluid. Viscosity acts on fluid-fluid interaction and also fluid- solid interaction, according to the nature of viscous behaviour of the fluid, fluids are classified.
Also there can be fluid forces (flow energy) involved with the motion caused by agitation through the churning device.

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