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### Course: Middle school physics>Unit 1

Lesson 2: Forces and acceleration

# Force, mass and acceleration

When a net force acts on an object the object's motion will change in the direction of this net force. The larger the force is that acts on an object, the larger the change in motion. However, the greater the mass of the object, the greater the force needed to have the same change in motion. Created by Sal Khan.

## Want to join the conversation?

• Im confused. There is no gravity in space so how will the asteroids weigh anything. So the asteroid with one rocket each will go at the samed speed..... right?
• Weight and mass are not the same thing.

All matter (you, the earth, astroids, and the sun, etc) has mass, but unless they're under the influence of gravity they won't have a weight.

For example, your weight on the moon is much less than your weight on earth, but your mass is always the same everywhere.

Here are the proper definitions:
- Mass: is the measure of the amount of matter in a body.
- Weight: is the measure of the amount of force acting on a mass due to the acceleration of gravity.
• at , I don't understand the term 'force equals mass times acceleration. could some one please explain? thanks.
• They say that because The amount of F (Lets say force is F) depends on how much mass the object has and how much acceleration is acting on it. Let's say that a ball has a mass of 100 grams. And there is another ball that weighs 50 grams. You push each ball with enough force to push a ball that weighs 200 grams. The first ball would move half as fast as the second because 50 is half of 100.

Did that help?
• Wouldn't adding more rockets add more weight also like the rock with 2 boosters should be going a bit slower than the big rock right?
• Not exactly, I think he's talking about the rockets in a way that the weight of the rocket doesn't matter. But your also right, the weight of the rockets will affect how fast the rocks are going, because the rocket engine also needs to carry the weight of the actual rocket, which would make the rocket go slower (and if there's a certain speed those rocks need to be going, the rockets need to generate more force). Basically what we're talking about is the power/weight ratio.

Good question.
• I'm here early lol
if the mass increases, then doesn't the force increase as well because F= ma and the bigger m gets the bigger F gets
(1 vote)
• Yes, you need a bigger force to get a bigger mass to undergo the same acceleration.
• Can somebody please explain to me more clearly what a net force is?
• Net force is the total amount of all force being acted on an object
• what can force change?
(1 vote)
• Force can impact quite a number of things. For example, if an object is in motion, a force applied may change it's speed or direction. Force can also stop or start making an object move.
If force is not applied on a moving object, that thing will move forever. That's why astronauts must be really careful about their movements in space. One wrong move, and they may never see Earth again.
Hope this helps! :D
• f=ma is like e=mc
(1 vote)
• Yes they're both formulas. The difference is that 'f=ma' is the formula of force and 'e=mc2' is the formula of energy.
• In space mass is neglected