2. Forces are pushes or pulls

3. Eg – gravity pulls everything downwards towards the centre of the Earth.

4. Forces are pushes or pulls Eg – gravity pulls everything downwards towards the centre of the Earth. Eg – if a book is sitting on a table, because gravity is pulling it downwards, the book pushes down against the surface of the table.

5. Forces are pushes or pulls Eg – gravity pulls everything downwards towards the centre of the Earth. Eg – if a book is sitting on a table, because gravity is pulling it downwards, the book pushes down against the surface of the table. Eg – on a windy day, the air pushes against a tree and could push it over.

6. Sometimes forces make an object change its motion.

7. A change in motion means that either the speed changes or the direction of the motion changes.

8. Sometimes forces make an object change its motion. A change in motion means that either the speed changes or the direction of the motion changes. A change in speed means acceleration/deceleration

9. Sometimes forces make an object change its motion. A change in motion means that either the speed changes or the direction of the motion changes. A change in speed means acceleration/deceleration Sometimes forces can change both speed and direction – eg when a ball is thrown into the air, gravity pulls it downwards so the ball travels slow on the way up, change direction, and then accelerate on the way down.

10. A force (F) has a size and a direction. The size of a force is measured in Newtons (N).

11. An arrow is used to show the direction of a force

12. A force (F) has a size and a direction. The size of a force is measured in Newtons (N). An arrow is used to show the direction of a force Forces act on everything. Often there is more than one force acting upon something and when this happens it is the combination of all the forces acting that affects the motion of the object.

13. A force (F) has a size and a direction. The size of a force is measured in Newtons (N). An arrow is used to show the direction of a force Forces act on everything. Often there is more than one force acting upon something and when this happens it is the combination of all the forces acting that affects the motion of the object. The combined force is called the net force Fnet.

14. A force (F) has a size and a direction. The size of a force is measured in Newtons (N). An arrow is used to show the direction of a force Forces act on everything. Often there is more than one force acting upon something and when this happens it is the combination of all the forces acting that affects the motion of the object. The combined force is called the net force F net. Forces acting in the same direction add together, while forces acting in opposite directions are subtracted.

15. When the forces on an object are unbalanced, the net force will make the object accelerate.

16. F net = maF net is the combined force,in N  m is the mass, in kg  a is the acceleration, in ms -2

17. 1. A pile of books, with a mass of 1.5kg is resting on a bench. When the books are pushed, they accelerate at 2 ms -2. Calculate the net force of the books. 2. When a single book of mass 500g is pushed, it accelerates at 3 ms -2. Calculate the net force on the book. (Remember you MUST convert the mass from grams into kilograms) 3. Joe pulls his bag along the floor, and the net force on the bag is 12N. The mass of the bag is 4kg. Calculate the acceleration of the bag.

18.  When different net forces are applied to objects of the same mass, a greater net force produces a greater acceleration. Eg – When Joe pulled a 4kg bag along the floor with a force of 12N, the acceleration was 3ms -2. When Peter pulled Joe’s bag, the net force on it was 24N. Calculate Peter’s acceleration of the bag.

19.  When different net forces are applied to objects of the same mass, a greater net force produces a greater acceleration. Eg – When Joe pulled a 4kg bag along the floor with a force of 12N, the acceleration was 3ms -2. When Peter pulled Joe’s bag, the net force on it was 24N. Calculate Peter’s acceleration of the bag. Fnet/m = 24/4 = 6ms -2 * Twice the force produces twice the acceleration.

20.  When the same force is used to accelerate two different masses, the smaller mass has the greater acceleration.

21.  Eg – Jack pulls a six pack of coke which has a mass of 2.5kg towards him. The net force on the cans is 4N. He takes 3 cans out and pushes the half-empty pack away. Again the net force on the cans is 4N.  Calc. the acceleration of the full pack.  Calc. the acceleration of the half empty pack.

22.  Mia has a toy trolley she likes to pull around. The diagram below shows the forces of Mia and her sister Edith pulling on a trolley and their brother, Callum, pulling in the opposite direction. What single force will have the same effect as all three children? Give the size and direction of this single force. 4N  2N  3N

23. Mia and her sister push the trolley as shown in the diagrams that follow. State the size and direction (right or left) of the combined force of the two sisters. a) 10N   12N b) 2N   4N c) 3N   15N c) d) 10N   30N 

24.  The starter motor on a car would not work. To start the car, a girl got 3 of her friends to push it. Each of the friends pushed the car with a force of 450N. Friction can be ignored in this case.  If the car with the girl driving inside it had a mass of 900kg, calculate the car’s acceleration.