Energy Transferred by Heating
Energy and Thermal Physics

Hammering lead to warm it up

Practical Activity for 14-16 PRACTICAL PHYISCS

Demonstration

Working mechanically to raise the temperature of different components.

Apparatus and Materials

  • Blunt drill bit
  • Electric drill
  • Brick and G-clamp
  • Piece of sheet lead
  • Hammer and hardwood anvil
  • Iron wire to hold piping
  • Bicycle pump

Health & Safety and Technical Notes

Read our standard health & safety guidance


Procedure

  1. Clamp the brick over a scrap of softwood to the bench.
  2. Bore a hole in the brick with the blunt drill, then pass the drill bit round so that it can be felt.
  3. Push the stiff iron wire through the lead piping and bend the end so as to hold the lead.
  4. Hammer the lead violently so that its temperature rises. A piece of lead sheet may be used instead of the piping, as shown in the diagram.
  5. Ask students to push in the piston of a bicycle pump quickly whilst holding a finger on the outlet so that they can feel the heating.

Teaching Notes

  • In all these demonstrations the components warm up. When the action stops, all the energy of the moving parts stored kinetically has been transferred to the components, so increasing the energy stored thermally.
  • The bicycle pump warms up because the speed of the air molecules inside the cylinder has increased. Momentum is transferred from the moving piston to the air molecules in the same way as hitting a ball with a moving bat transfers momentum. An increase in the speed indicates and increase in energy stored thermally. The temperature rises.
  • There are occasions when energy is transferred to a body but its temperature does not rise. If a beaker of crushed ice is melted with a Bunsen flame, the resulting slush remains at freezing point. In this case the heating increases potential energy in the force-fields of the molecular structure, as the molecules are pulled apart against the forces of mutual attraction that hold them in a solid crystal. The energy needed to do this is known as latent heat. (The term is too well established to think of calling it anything else - but beware of the word heat.)

This experiment was safety-tested in November 2005

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