Mechanical energy is the energy that is possessed by an object due to its motion or due to its position. Mechanical energy can be either kinetic energy (energy of motion) or potential energy (stored energy of position).
We use a system consisting of two weights hanging at each end of a thin thread lying over a wheel. A photo gate is placed so that the light is interrupted by the spokes of the wheel. The data are recorded electronically and this makes it possible to calculate the kinetic and gravitational potential energy of the weights. Setup:
The experiment is made in common.
The small weight is held on the floor at the start. Start the data collecting a split second before the small weight is allowed to rise. The movement is stopped just before the large weight hits the floor.
Measurements and calculations:
Measure the initial height of the large weight.
The system measures the distance s that is the movement of the thread from the start. So the height is equal to s. The system also calculates the speed. The zero point of the potential energy is chosen to be at floor level.
m=small blue weight
(0.1 kg) (Initial height = 0 m)
M= big red weight
(1.12 g) (Initial height= 1.746 m)
Potential energy is stored energy of position ready to be used. You can think of potential energy like a car stopping for red light. The car is ready to move. Or when an object is lifted. The higher the object the more potential energy is produced. In that way it will also form more kinetic energy when the object is dropped. Gravitational potential energy (PE) = mass × gravity × height (g = 9.82 m/s2)
PE (m) = 0.1 kg × 9.82 m/s2 × 0 m
PE (m) = 0 Joules
PE (M) = 0.12 kg × 9.82 m/s2 × 1.746 m
PE (M) = 2.06 Joules
PE (M,m) = 0+2.06=2.06
In order for potential energy to be used it must be turned in to one of the six forms of kinetic energy. If we look at the example with the car from before. The potential energy is turned in to kinetic energy as soon as the car starts to move. Kinetic energy (KE) = ½*m*v^2+½*M*v^2
Mechanical energy (ME) = Kinetic energy + Gravitational potential energy.
We can see in the graph that gravitational potential energy is steadily decreasing and kinetic energy is steadily increasing. Because PE and KE are not similar we expect the mechanical energy to be horizontal therefore in theory it should be constant. As we see this is not the case here. The mechanical energy line is...
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