thermal Our body contains potential energy from food we have eaten. kinetic This potential energy is transformed into the energy of our hands and chemical arms as we rub our hands together. As our hands move past each other and rub against each other, friction allows the energy to be transformed into energy on the surface of our hands.

When the metal ring and metal sphere in Figure CQ19.8 are both at room temperature, the sphere can barely be passed through the ring, (a) After the sphere is warmed in a flame, it cannot be passed through the ring. Explain, (b) What If? What if the ring is warmed and the sphere is left at room temperature? Does the sphere pass through the ring?

Rubbing your hands together warms them by converting work into thermal energy. If a woman rubs her hands back and forth for a total of 20 rubs, at a distance of 7.50 cm per nub, and with an average frictional force of 40.0 N, what is the temperature increase? The mass of tissues warned is only 0.100 kg, mostly in the palms and fingers.

Suppose a person is covered head to foot by wool clothing with average thickness of 2.00 cm and is transferring energy by conduction through the clothing at the rate of 50.0 W. What is the temperature difference across the clothing, given the surface area is 1.40 m2?