Question

The diagram shows a swinging pendulum.

A pendulum hanging from a bar is shown in 3 positions. 1 is swung to the right, 1 to the left, and 1 in the middle. Solid lines connect the bob to he support in the right and left positions. A dotted line connects the bob to the support in the center position. Dotted lines connect right, left, and center along the arc of the pendulum swing.

Which best explains what happens to the motion of the pendulum due to the law of conservation of energy?

The pendulum will slow down and eventually stop moving as the mechanical energy transforms to thermal energy.
The pendulum will continue moving at the same speed because mechanical energy is created as the pendulum moves.

Answer 1

The first statement is correct.

As the pendulum swings, gravitational potential energy converts to kinetic energy and back. In a real pendulum friction and air resistance do work, converting mechanical energy into thermal energy, so the mechanical energy (and thus the amplitude and speed) decreases over time and the pendulum eventually stops. Energy is conserved overall, but it is transferred into thermal energy, not created.