1. Newton’s Laws of Motion Newton’s First Law If there is no unbalanced force an object will move at constant velocity or remain at rest. Newton’s Second Law F u = ma Newton’s Third Law Every force has an equal but opposite reaction force. Eg. Force of the rocket on the hot gases = - Force of the hot gases on the rocket

2. Balanced Forces Forces are balanced when they are equal in size but opposite in direction. If everyone pulls with the same strength there will be no movement. Forces are balanced. pull Buoyancy of water weight Forces balanced so no up down movement Bigger downward force boat moves down

3. For balanced forces there is no change in movement. Force due to water - buoyancy Force due to gravity - weight Going down Going up

4. Balanced Forces Object will be moving at constant speed or be at rest. Terminal speed thrust weight lift Air resistance

5. Parachute weight is constant weight Air resistance No air resistance weight Air resistance Just left the plane No speed, no air resistance. Downward unbalanced force – accelerate down Speeding up, air resistance increasing. Unbalanced force is smaller so less acceleration. Maximum speed ( terminal velocity) Air resistance = - weight so no unbalanced force No acceleration Draw a speed time graph for a parachute jump Sky diver

6. weight Air resistance weight Air resistance Land !!! Speed is now zero As speed decreases so does air resistance until the forces are balanced and terminal velocity is reached. The parachute is opened and air resistance increases. Upward unbalanced force, so the parachute decelerates and slows down Tutorial Qus page 5/6 Free falling objects.

7. Example 1.A car of mass 5000 kg is travelling at constant speed. The engine exerts a force of 20 N. (a) What is the magnitude of the friction forces? (b) The engine force increases to 100N. What is the car’s acceleration? Assume the friction forces stay constant. Tutorial Questions pages 14 and 15 Qus 1 to 8

8. Rockets 2. A rocket of mass 10 000kg was launched from the Earth. (a)If it had an initial acceleration of 2ms -2, what would the force of the rockets be? (b)As it moves away from the Earth, the acceleration increases, give two reasons why.

9. Lifts 3. A person of mass 60 kg stands on scales inside a lift. The lift accelerates at 4 ms -2 downwards. What will be the reading on the scales? Tutorial Questions 15 to17 Qus 9 to15 Purple book Chp 2.5

10. Connected Masses 4.4. A force of 20 N is used to pull the blue box, mass 5 kg. Friction is 1N on each mass. The green box has a mass of 1.5 kg and the grey box has a mass of 2 kg. What is the acceleration of the blocks? What will be the tension between the green and blue boxes? Tutorial Questions pages18 and 19 Qus 16 to 19

11. Connected Masses 2 5. Assume no friction (a)What is the acceleration of the 0.5 kg trolley? (b)What is the tension in the string? 0.5 kg 1 kg Tutorial Questions page 19 Qu 20 Purple book Ex 2.2

12. Forces at Angles 40 N 45 0 6. If the object has mass, 1500 Kg, what will its acceleration be? Tutorial Questions pages 19 to 22 Qus1 to 5

13. Forces and Slopes 20 0 7. A mass of 10 kg is sliding down a slope. If it accelerates at 2ms -2, find:- (a)The component of the weight acting down the slope. (b)The friction between the mass and the slope. Tutorial Questions pages 19 to 22 Qus1 to 9 Purple book Chp 2.4 FwFw 20 0 Fc