Listen&Learn: Escape velocity

Learn how fast objects need to travel to reach outer space

Pre-listening vocabulary

• gravity: the natural force that keeps objects on the surface of a planet
• minimum: the smallest possible amount of something
• mass: the amount of matter that an object contains
• increase: to grow larger
• infinite: never-ending, impossible to count
• density: the amount of mass that is contained in a unit of space

Listening activity

Podcast: Play in new window | Download (Duration: 1:25 — 1.3MB)

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Gapfill exercise

Every source of gravity in the universe has an escape velocity. This is the minimum constant speed that an object has to to fully escape from a planet or and enter outer . For an object of any mass to be launched into space from Earth, it must be travelling at approximately 11.2 km/s, or 40,000 km/h. To determine escape velocity, scientists need to know the mass and radius of the source of gravity. Escape velocity increases for planets and stars with more mass. It would be easier to launch something from the Moon than from Earth. For a black hole, which has infinite density, the escape velocity is greater than the speed of . This is why can possibly escape from its gravity.

Comprehension questions

See answers below

1. The escape velocity is
   a. the maximum mass of an object travelling into space
   b. the minimum mass of an object to be a strong source of gravity
   c. the minimum constant speed of an object travelling into space
   
2. The escape velocity of Earth is about
   a. 9.8 km/s
   b. 11.2 km/s
   c. 40,000 km/s
   
3. It would be easiest to launch an object from
   a. Earth
   b. the Moon
   c. a black hole

Discussion/essay questions

1. Reaching outer space was an important achievement in human history. What kinds of space exploration do you think will be possible in the future?

Transcript

Every source of gravity in the universe has an escape velocity. This is the minimum constant speed that an object has to travel to fully escape from a planet or star and enter outer space. For an object of any mass to be launched into space from Earth, it must be travelling at about 11.2 km/s, or 40,000 km/h. To determine escape velocity, scientists need to know the mass and radius of the source of gravity. Escape velocity increases for planets and stars with more mass. It would be easier to launch something from the Moon than from Earth. For a black hole, which has infinite density, the escape velocity is greater than the speed of light. This is why nothing can possibly escape from its gravity.

Answers to comprehension questions

1c 2b 3b