![]() Gravity – The force of attraction between objectsįor example, the mass of an astronaut is the same whether on the Earth, the moon or in outer space because there is the same amount of matter in the body of the astronaut.Weight - The force on an object due to gravity.Mass - The amount of matter in an object.If you throw the same object on the Earth, air resistance slows it down and gravity pulls it to the ground where it then experiences friction, bringing it to a stop. If an astronaut throws an object in space it will continue moving at a constant speed because there is no air resistance to slow it down. Therefore, your body will continue moving forwards until it experiences a force slowing it down (eg from the road ahead). Unbalanced forces = change in motion (this could be speeding up, slowing down or changing direction)įor example, the reason you are thrown forwards in a head-on collision is that objects continue in their current state (rest or constant speed) unless acted on by a resultant force.Balanced forces = no change in motion (this could mean the object is not moving OR that it is moving at a constant speed).Newton’s 1st law of motion states that an object will stay at rest, or continue at a constant speed, unless it is acted on by an unbalanced force. The resultant force is the sum of all the forces acting on an object. On any object, there are usually multiple forces acting. Therefore the wheels spin and spray mud backwards but the car does not move forwards. However, the mud is unable to produce a reaction force to push the car forwards. If a car is driving on softer ground, such as mud, the wheel still exerts a force on mud backwards. ![]() ![]() The recoil force on a gun (the gun recoils back to the shooter as the bullet is fired)Įxhaust gases used to provide thrust for a rocket This is because the floor exerts an equal and opposite force on you, holding you up. Gravity is pulling you down towards the centre of the earth but, at this moment you are (probably) not moving down through the floor. Non Contact Force - The objects are not touching, i.e.:Įvery action has an equal and opposite reactionįor example, if you push against a wall, the wall must be producing an equal and opposite force on you otherwise the wall would fall over or your hand would go through the wall. Newton's Laws of Motion Newton’s Laws of Motionįorces can be categorised as contact or non-contact forces:Ĭontact Force - The objects are touching, i.e.:
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