## 7 (b.a.) Kinetic and Potential Energy

Transformations Between Potential and Kinetic Energy

One of the most common energy transformations is the transformation between potential energy and kinetic energy. In waterfalls such as Niagara Falls, potential energy is transformed to kinetic energy. The water at the top of the falls has gravitational potential energy. As the water plunges, its velocity increases. Its potential energy becomes kinetic energy.

Energy Transformation in Juggling

Any object that rises or falls experiences a change in its kinetic and gravitational potential energy. Look at the orange in Figure 11. When it moves, the orange has kinetic energy. As it rises, it slows down. Its potential energy increases as its kinetic energy decreases. At the highest point in its path, it stops moving. Since there is no motion, the orange no longer has kinetic energy. But it does have potential energy. As the orange falls, the energy transformation is reversed. Kinetic energy increases while potential energy decreases.

Energy Transformation in a Pendulum

In a pendulum, a continuous transformation between kinetic and potential energy takes place. At the highest point in its swing, the pendulum in Figure 12 has no movement, so it only has gravitational potential energy. As it swings downward, it speeds up. Its potential energy is transformed to kinetic energy. The pendulum is at its greatest speed at the bottom of its swing. There, all its energy is kinetic energy.

As the pendulum swings to the other side, its height increases. The pendulum regains gravitational potential energy and loses kinetic energy. At the top of its swing, it comes to a stop again. And so the pattern of energy transformation continues.

Energy Transformation in a Pole Vault

A pole-vaulter transforms kinetic energy to elastic potential energy, which then becomes gravitational potential energy. The pole-vaulter you see in Figure 13 has kinetic energy as he runs forward. When the pole-vaulter plants the pole to jump, his velocity decreases and the pole bends. His kinetic energy is transformed to elastic potential energy in the pole. As the pole straightens out, the pole-vaulter is lifted high into the air. The elastic potential energy of the pole is transformed to the gravitational potential energy of the pole-vaulter. Once he is over the bar, the pole-vaulter’s gravitational potential energy is transformed back into kinetic energy as he falls toward the safety cushion.

What kind of energy lifts a pole-vaulter over the bar?

One of the most common energy transformations is the transformation between potential energy and kinetic energy. In waterfalls such as Niagara Falls, potential energy is transformed to kinetic energy. The water at the top of the falls has gravitational potential energy. As the water plunges, its velocity increases. Its potential energy becomes kinetic energy.

Energy Transformation in Juggling

Any object that rises or falls experiences a change in its kinetic and gravitational potential energy. Look at the orange in Figure 11. When it moves, the orange has kinetic energy. As it rises, it slows down. Its potential energy increases as its kinetic energy decreases. At the highest point in its path, it stops moving. Since there is no motion, the orange no longer has kinetic energy. But it does have potential energy. As the orange falls, the energy transformation is reversed. Kinetic energy increases while potential energy decreases.

Energy Transformation in a Pendulum

In a pendulum, a continuous transformation between kinetic and potential energy takes place. At the highest point in its swing, the pendulum in Figure 12 has no movement, so it only has gravitational potential energy. As it swings downward, it speeds up. Its potential energy is transformed to kinetic energy. The pendulum is at its greatest speed at the bottom of its swing. There, all its energy is kinetic energy.

As the pendulum swings to the other side, its height increases. The pendulum regains gravitational potential energy and loses kinetic energy. At the top of its swing, it comes to a stop again. And so the pattern of energy transformation continues.

Energy Transformation in a Pole Vault

A pole-vaulter transforms kinetic energy to elastic potential energy, which then becomes gravitational potential energy. The pole-vaulter you see in Figure 13 has kinetic energy as he runs forward. When the pole-vaulter plants the pole to jump, his velocity decreases and the pole bends. His kinetic energy is transformed to elastic potential energy in the pole. As the pole straightens out, the pole-vaulter is lifted high into the air. The elastic potential energy of the pole is transformed to the gravitational potential energy of the pole-vaulter. Once he is over the bar, the pole-vaulter’s gravitational potential energy is transformed back into kinetic energy as he falls toward the safety cushion.

What kind of energy lifts a pole-vaulter over the bar?