Word Bank: terminal velocity, weight, inertia, force Weight = mass * acceleration due to gravity

1. 
   _________________ is a push or pull that give energy to an object
   
2. 
   _________________ is the property of matter that tends to resist any change in motion
   
3. 
   When a falling object no longer accelerates, it has reached its _______________________________
   
4. 
   _________________ is a measure of the force of gravity on an object.
   

Our everyday lives involve such activities as sitting, walking, picking up things from the ground and lying in bed. None of these activities are possible in orbit. Once a spacecraft reaches orbit, everything inside it appears to be weightless. Anything (or anyone) that is not tied down will float.

Astronauts first feel the effect of weightlessness when the rocket engines are turned off. Straight away, they begin to float, held down only by seatbelts. Weightlessness allows astronauts to appear super-strong. They can lift objects that would be far too heavy to move on Earth. But there are some drawbacks.

Without the effect of gravity, blood and other body fluids begin to flow towards the head. This can cause a feeling of stuffiness and headaches. With no gravity to push against, bones and muscles can become weak. To stay fit, they have to exercise several hours each day. This allows them to recover more quickly when they return to Earth.

In a shuttle or space station, there is no up or down. There is no difference between a floor and a ceiling. This can make astronauts feel sick until they get used to this strange arrangement.

So, why doesn’t the Space Station or satellites in orbit fall to the Earth, and why do the astronauts and objects inside the ISS or other spacecraft appear to be floating? Because of speed!

The astronauts, the ISS itself and other objects in Earth orbit aren’t floating, they are actually falling. But they don’t fall to the Earth because of their huge orbital velocity. Instead, they fall around Earth. Objects in Earth orbit have to travel at least 28,160 km/h (17,500 mph). So, as they accelerate towards the Earth, the Earth curves away beneath them and they never get any closer. Since the astronauts have the same acceleration as the space station, they feel weightless.

Newton’s Third Law: Action and Reaction

https://www.youtube.com/watch?v=NfuKfbpkIrQ

7. 
   Give another example of Newton’s 3^rd law.
   

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