1. is defined as a push or a pull A force is defined as a push or a pull

2. All Forces Have… 1. DIRECTION - Forward against a big rock -Right, towards a magnet - Down towards the Earth (gravity )

3. All Forces Have… 2. MAGNITUDE – Also known as SIZE or AMOUNT of force!!! Scientists measure forces using a unit called the newton (N) Scientists measure forces using a unit called the newton (N) This is the amount of force it takes to accelerate 1 kilogram of mass 1 m/sec 2 This is the amount of force it takes to accelerate 1 kilogram of mass 1 m/sec 2 1 kg 1 m/sec2 1 newton

4. Gravity pulls 1 kilogram with a force of 9.8 newtons. Gravity pulls 1 kilogram with a force of 9.8 newtons. ….. So a 100 kg mass is being pulled with a force of 980 newtons! ….. So a 100 kg mass is being pulled with a force of 980 newtons! 100 kg 1 kg

5. Force is measured with a tool called a spring scale

6. Combining forces When two forces are exerted on an object in the same direction, their magnitude is added – giving net force. When two forces are exerted on an object in the same direction, their magnitude is added – giving net force. If each of these people pull with a force of 100 N to the left, their forces are combined for a net force of 400 N! If each of these people pull with a force of 100 N to the left, their forces are combined for a net force of 400 N! 1oo N 4oo N

7. Any object that is standing still has balanced forces acting on it. If two teams pull on a rope with the same force, they don’t move! If two teams pull on a rope with the same force, they don’t move! Gravity is acting on an object that is sitting still – pulling it down. Gravity is acting on an object that is sitting still – pulling it down. If this was the only force, the object would be sinking. If this was the only force, the object would be sinking. Other forces push back! Other forces push back!

8. Elastic force Compression – force of being pushed together Compression – force of being pushed together the object withstands being squashed the object withstands being squashed the force of the Earth pushing back up against gravity! the force of the Earth pushing back up against gravity! Earth pushes back against gravity!

9. Tension – force of being pulled apart Steel cables on a bridge experience great tension force Steel cables on a bridge experience great tension force As does the rope in a tug of war! As does the rope in a tug of war!

10. Unbalanced forces Produce changes in motion. Produce changes in motion. If a golfer hits a ball, the force of his club is greater than the other forces on the ball, creating unbalanced forces and making the ball move! If a golfer hits a ball, the force of his club is greater than the other forces on the ball, creating unbalanced forces and making the ball move! Gravity Compression Force from Club

11. Gravity Is a result of mass Is a result of mass – The more mass an object has, the more gravity it has! – The more mass an object has, the more gravity it has! Stars and planets have HUGE mass, and huge gravity. Stars and planets have HUGE mass, and huge gravity. Even you have gravity – it’s just so small that it doesn’t have much effect. Even you have gravity – it’s just so small that it doesn’t have much effect. Earth has much greater mass - so it has much more gravity. Earth has much greater mass - so it has much more gravity.

12. Stars, planets, and the Solar System. All are formed by gravity. All are formed by gravity. Gravity also maintains the shape of these objects Gravity also maintains the shape of these objects Gravity tugs from the center inward Gravity tugs from the center inward This forms the shape of planets and stars - a ball! This forms the shape of planets and stars - a ball! The Solar System forms a disk The Solar System forms a disk