Power
Energy and Thermal Physics

Climbing stairs

Practical Activity for 14-16 PRACTICAL PHYISCS

Class practical

Estimating the change in energy stored gravitationally in climbing a flight of stairs.

Apparatus and Materials

  • Bathroom scales
  • Tape measure, 5 m

Health & Safety and Technical Notes

Since this activity does not require the time taken to be measured, a delegation could measure the height while the class remains in the laboratory or classroom.

Read our standard health & safety guidance


Procedure

  1. Each student must know their mass in kilograms, use the scales to determine it, or use an 'mass of an average person'.
  2. Measure the height of the stairs from the ground floor to the top of the highest step.
  3. Each student climbs the flight of stairs and calculates the increase in the energy stored gravitationally.

Teaching Notes

  • When someone climbs the stairs energy is transferred from their muscles (energy stored chemically in food and oxygen) to be stored gravitationally. The change to the energy stored gravitationally can be calculated using the equation: change in energy stored gravitationally = mgΔh.
  • Where mg is the weight of the climber and QuantitySymbol{Δh} is the vertical distance climbed.
  • You may need skills in crowd control if other classes are not to be disturbed and students are not to get hurt. Students may try to turn this experiment into a demonstration of power, by timing how fast they can get to the top of the stairs!
  • Students may also ask why they feel fatigued when they hold up a load but the load doesn't move. In order to grip the load, muscles are kept tensed; they squeeze the blood vessels and restrict blood flow. As a result the chemical products of muscular activity accumulate and are not washed away so quickly by the blood. This accumulation of chemical products makes the nerves give a sense of fatigue. So the feeling of fatigue is chiefly an indirect result of the muscle tension.
  • The continuing demand while you hold a load at rest arises from the muscle fibres developing tension very rapidly. In a large muscle, fibre after fibre is fired into tension as a nerve impulse arrives but each fibre soon relaxes. Later on it renews its tension again. So the steady pull of a muscle is really the result of many brief tugs, a dynamic force. The sum total of these pulses of force shows tiny statistical fluctuations like a trembling effect.
  • There is a transfer from energy stored chemically to energy stored thermally. Releasing the tension does not transfer energy back to the muscles.

This experiment was safety-tested in January 2006

Power
appears in the relation P=VI P=I^2R P=V^2/R ΔQ=PΔt
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