# Throwing a ball horizontally on the moon and pushing it in the spacestation

Why is there a difference in force required throwing a ball horizontally on the moon and pushing it horizontally it in the spacestation
Thanks

## Answers and Replies

JBA
Science Advisor
Gold Member
The mass and inertia of the ball is the same at both locations so no force difference there; however, there is an atmosphere maintained in the space station and therefore an aerodynamic drag resistance, whereas there is very little atmosphere on he moon so there is essentially no aerodynamic drag resistance there.

Janus
Staff Emeritus
Science Advisor
Gold Member
Why is there a difference in force required throwing a ball horizontally on the moon and pushing it horizontally it in the spacestation
Thanks
The first question would be: What difference are you referring to?

• nasu
Thank you; I will try to be more clear, taking gravity away from all.
On the moon the astronaut requires the same force to throw the ball horizontally in the space station as the astronaut would on Earth.
On the space station would it require the same force to move a ball one meter, as it would to move the same ball horizontally one meter on Earth/ the Moon in the absence of friction and air pressure?

Thanks for your patience!
Martyn Arthur

Nugatory
Mentor
On the space station would it require the same force to move a ball one meter, as it would to move the same ball horizontally one meter on Earth/ the Moon in the absence of friction and air pressure?
Force doesn't move things, it changes their speed. The relevant equation is Newton's second law ##F=ma##; ##m## is the same in both cases so the same force will change the speed (##a## is the acceleration and that's just another word for "change of speed") by the same amount. And once you've started it moving, in the absence of friction and air resistance it will keep moving, so no matter how small a force you apply for how short of a time if you wait long enough it will have moved one meter.

• PeroK
sophiecentaur
Science Advisor
Gold Member
2020 Award
Could it be that the OP is talking about launching the same object so that it travels parallel with the surface of the Moon / Earth? It strikes me that the object would already be travelling horizontally in the space station if it's in a circular orbit so no force would be needed. If it's on the Moon's surface then you would need to accelerate it until it is in, effectively, a circular orbit at zero height above the surface. The Force needed would depend on how long or over what distance it acted so more information would be needed.

FactChecker
Science Advisor
Gold Member
Thank you; I will try to be more clear, taking gravity away from all.
On the moon the astronaut requires the same force to throw the ball horizontally in the space station as the astronaut would on Earth.
Any amount of force in the horizontal direction will "throw the ball horizontally". So this is a misleading statement.
On the space station would it require the same force to move a ball one meter, as it would to move the same ball horizontally one meter on Earth/ the Moon in the absence of friction and air pressure?
Any amount of force would start a ball moving in the horizontal direction. How far it will move is just a matter of how long you let it move. So this question can not be answered.

Only thing I see is if you are trying to get the ball to go 1 m before it hits the ground, you need to consider where it hits the ground. The horizontal force required to get the ball of fixed mass up to fixed horizontal velocity is essentially constant (ignoring air resistance), but the vertical acceleration is set by gravity. For a frictionless, elastic ball, the horizontal velocity doesn't change on impact with the ground (assuming a flat surface), so (it seems to me), the force required in all cases is constant if you care only about how fast the ball goes horizontally. If the ball needs to get over a mark on the ground 1m away, the required force (terminal horizontal velocity) on the ball increases with gravity.