ROCKETS AND SATELLITES

Key Concepts•How does a rocket lift off the ground?•What keeps a satellite in orbit?

Key Terms•Satellite•Centripetal force

HOW DO ROCKETS LIFT OFF?

Rockets lift off because of Newton’s third Law

They burn fuel and push exhaust gases downward at a high velocity

The gases push upward on the rocket with an equal but opposite force

This upward pushing force is called thrust

Thrust must be greater than gravity for the rocket to rise and accelerate into space

WHAT IS A SATELLITE?

Any object that orbits another object in space

Our moon is a natural satellite

Artificial satellites are launched into orbit

Used for communications, military intelligence, weather analysis and geographical surveys

The ISS (International Space Station) is an example of an artificial satellite

CIRCULAR MOTION

Artificial satellites travel around Earth in almost circular path

An object moving in a circular path is accelerating because it is constantly changing direction

If an object is accelerating, a force must be acting on it – called centripetal force

Centripetal means center seeking The Earth’s gravity is the centripetal

force for the satellite. It keeps pulling the satellite towards the Earth

SATELLITE MOTION

Q: Why don’t satellites fall to Earth like a thrown ball does?

A: They have a greater horizontal velocity than a ball thrown on Earth

EXPLANATION:

A ball thrown has horizontal force moving it forward. Gravity is a force acting to pull it to the ground. The more force you give the ball the faster it travels horizontally and the greater distance it travels before hitting the Earth

A satellite in orbit around the Earth is continuously falling towards the Earth, but because the Earth is curved and they are traveling so fast , they don’t hit but travel around it

A satellite is a falling projectile that keeps missing the ground!!

SATELLITE MOTION

A satellite does not need fuel because it continues to move ahead due to its inertia

Gravity continuously changes its direction

The speed required to keep a satellite in orbit is 7,900m/s

SATELLITE LOCATION

Mapping and observation satellites are put into low orbits of less than 1,000 km

Completes an orbit in less than 2 hours Satellites such as communications satellites

put into higher orbits (36,000 km) where they circle the Earth in 24 hours Because of this they remain over the same point on Earth –

Geosynchronous orbit

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File:Centripetal_force.PNG http://www.stockcarscience.com/scienceTopics/

scsRacing_CentrifugalForce.php http://www.spacetoday.org/Satellites/

YugoWarSats.html http://www.nasa.gov/mission_pages/station/

multimedia/sts114_7200.html http://exploration.grc.nasa.gov/education/rocket/

rktth1.html