This time when the trolley is given a push, it travels with constant velocity v down the compensated runway until halfway down.The ticker-tape is also fixed to the reverse end of the trolley so that it runs out behind the trolley and passes through the ticker-timer. Because the thread is slack it will not stay in a pulley groove, and so a length of glass tube or knitting needle should be used as a roller. This time start the trolley at the end of the trolley board nearest the pulley, with the thread slack. The thread should be attached to the trolley and carry a 100 g weight hanger as before. Compensate the runway for friction the opposite way round.The experiment can be repeated but in reverse, using the trolley to raise the load.However, if the demonstration is carried out slowly, and as many energy losses as possible are accounted for, then the two values should be close enough to satisfy the students. As a result of friction, energy will always be stored thermally in the surroundings. It is impossible to demonstrate the principle of conservation of energy for thermodynamic reasons.warming the pulley, and the wheel bearings, the air. How reliable is the experiment? Where do students think that the energy might have been transferred to? Some energy will be stored thermally s, e.g. Compare this with the change in energy of the load stored gravitationally, Δ E = m × g do not agree.Measure the mass of the trolley on the balance. Estimate the value of v from the ticker-tape.After this, the trolley will move with constant velocity v. Release the trolley, so that the falling mass accelerates it until the mass hits the ground.Pass the other end through the ticker-timer. Attach a length of ticker-tape to the trolley.The length of thread must be long enough for the mass hanger to hit the ground well before the trolley reaches the end of the runway. ![]() Thread it over the pulley and tie it to the mass hanger. Attach a length of thread to the trolley.Do this by raising one end of the board so that the trolley, once started, will continue at constant speed as judged by the equal spacing between ticker-tape dots. Compensate it for friction in the normal way. Clamp the pulley to the end of the runway.
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