- 1). Measure the distance from the tabletop to the bottom of the pendulum when it is at rest. This is the zero point, i.e., the height it is at at the bottom of its arc. It is at this point that the pendulum will have maximum kinetic energy and minimum gravitational potential energy.
- 2). Measure the distance from the tabletop to the height the pendulum will be raised to when it is released to start its swing. This is the top of its arc, or the point where it has no kinetic energy and maximum gravitational potential energy.
- 3). Subtract the height of the top of the arc from the height of the bottom of the arc. This is the vertical distance the pendulum will fall. The reason that the height of both the top and bottom of the arc are measured from the table instead of just measuring the distance of the fall directly is that when the pendulum falls it moves horizontally as well as vertically. It can be more difficult and less accurate to try to estimate a vertical distance between two points that are not lined up horizontally.
- 4). Multiply the distance the pendulum will fall by the acceleration due to gravity. If you measured the heights in meters, then use 9.8 for the acceleration. This is the number of meters per second a falling object gains every second. If you measured in feet then use 32, which is the number of feet per second that it gains every second.
- 5). Multiply the result of the last step by two and then take the square root of the result. This is the velocity of the pendulum the moment it hits the bottom of its arc in either meters per second or feet per second. If it hit something, this is the impact velocity.
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