# Who decides how long a second is? - John Kitching

## Important Vocabulary Words From The Video

To keep time is to tell time using a clock or other time-keeping device. You might use a clock to tell time when you're playing a game, or you might use a clock to tell time when you're working.

• The clock on the wall told them that it was 2:00 pm.
• The clock on the wall told them that it was 9:00 am.

The word unchanging refers to something that doesn't change. The sky is always unchanging, and the stars are always in the sky.

• The unchanging quality of the sky made it difficult for the photographer to capture the perfect photo.
• The unchanging quality of the laws made it difficult for the lawyer to change them.

To orbit is to go around a planet or a star. The Earth orbits around the sun.

• The satellite was orbiting the Earth.
• The planets were orbiting around the star.

When something is ticking, it's alive and constantly moving. You can hear it ticking if you hold it in your hand and let it go.

• The clock is ticking, and it's going to be time to wake up soon.
• The clock is ticking, and it's going to be time to go to bed soon.

Pendulums are devices that are used to measure the motion of objects. They are usually made out of metal, and they have a weight at the bottom.

• The pendulum was swinging back and forth, indicating that the weight was moving.
• The pendulum is swinging back and forth, indicating that the object is moving.

To vaporize something is to turn it into a vapor. When you vaporize something, you heat it up so that it becomes a gas.

• The scientist was trying to vaporize the virus so that it could be studied.
• The pilot was trying to vaporize the enemy planes, so that they would not be able to attack.

Oscillate means to move back and forth, to swing back and forth. When the price of a stock oscillates, it moves up and down a lot over a short period of time.

• The stock prices oscillated throughout the day.
• The oscillation of the fan blades creates a noise.

To rotate something is to turn it so that it is facing the opposite direction. This is usually done so that it can be used more efficiently.

• The machine needs to be rotated so that the blades are facing the right direction.
• The flag needs to be rotated so that the stars are facing the ground.