1. Mechanics Newton‘s Laws

2. Inertia

3. Inertia Inertia is the property of any mass to resist a change in motion (velocity or direction). Inertia is the property of any mass to resist a change in motion (velocity or direction). The larger the mass the higher the inertia of an object. The larger the mass the higher the inertia of an object. Examples: (Explain using the idea of inertia) Examples: (Explain using the idea of inertia) 1 Pulling a table cloth from under a set table 2Stopping / starting of a tram 3your example?

4. Inertia Objects aim to remain in the same state of motion: Objects aim to remain in the same state of motion: –At rest….. –Moving at a certain speed.

5. Newton‘s 1 st Law FILL IN THE BLANKS: FILL IN THE BLANKS: « A body will remain at _____ or continue in a __________ line at a _______ speed unless it is acted on by an __________ ______. »

6. Inertia If there is no resultant Force acting on an object the object either - remains at rest when at rest - When moving it keeps on moving at constant speed in a straight line

7. More Revision DefineForce: ‘Push, Pull’ experienced by an object Forces can only be recognized through their effect (Example: Deformation, change in speed, change in direction) Speed (Velocity): distance covered in a certain timeS/t (velocity includes direction) Acceleration change in velocity over timeΔV/t

8. Newton‘s 2 nd Law Revision : Copy and complete the table. QuantitySymbolUnit Unit Symbol ForceFNewton Massmkg Speed(Velocity) metre per second Accelerationa

9. Newton‘s 2 nd Law Investigating the Relationship between Force, Mass and Acceleration Experiment: (see instruction sheet) Force The weight (gravitational force) hanging over the pulley will accelerate the trolley. The light gate will measure the acceleration.

10. Experiment The acceleration needs to be measured before the weight hits the floor. The acceleration needs to be measured before the weight hits the floor. Start with the weights on the trolley and move them to the hanger. Start with the weights on the trolley and move them to the hanger. For each weight repeat the experiment three times to get an average. For each weight repeat the experiment three times to get an average. Repeat for five different weights. (more if you have time) Repeat for five different weights. (more if you have time) Put your results in the table. Put your results in the table.

11. Results Use your table of results to draw a graph. Use your table of results to draw a graph. If you don’t have a set of results use the ones in the table below. If you don’t have a set of results use the ones in the table below. AcceleratingForce(N) Acc1 (mms -2 ) AVE Acc (mms -2 ) 1 2 3 4 5

12. Results Use your table of results to draw a graph. Use your table of results to draw a graph. If you don’t have a set of results use the ones in the table below. If you don’t have a set of results use the ones in the table below. Force(N) Acc1 (mms -2 ) AVE Acc (mms -2 ) 1398404410 2802810790 3117812061214 4141014071390 5175018051813

13. Graph Plot the pointsPlot the points Draw the best fit line.Draw the best fit line. Take note.Take note. 1.The line is straight 2.It passes through the origin 3.This means that Force and Acceleration are directly proportional.

14. Graph Analysis / Conclusion As can be seen the graph is a straight line passing through the origin. As can be seen the graph is a straight line passing through the origin. This means that force and acceleration are DIRECTLY PROPORTIONAL This means that force and acceleration are DIRECTLY PROPORTIONAL F α a (mass was kept constant) F α a (mass was kept constant) Therefore F=ma for const. m Therefore F=ma for const. m Newton’s Second Law: Newton’s Second Law: The acceleration of a body is directly proportional to the applied force (for constant mass) Examples: (copy from board)

15. Newtons Second Law F =ma F =ma Can you write down the other two equations? a=F/m a=F/m m=F/a m=F/a F am Definition: Newton 1 Newton is the force that gives a mass of 1 kg an acceleration of 1m/s²

16. Example A car engine applies a force of 2500N on the car which has a mass of 1250kg. What is the acceleration of the car? A car engine applies a force of 2500N on the car which has a mass of 1250kg. What is the acceleration of the car? F = 2500N m = 1250 kg a = ? F =ma a = F/m a = 2500N/1250kg a = 2m/s 2 Try the problems on page 3 of your booklet!

17. Free Fall Any ‘free falling’ object has only the force of gravity acting on it. Any ‘free falling’ object has only the force of gravity acting on it. The force depends on The force depends on the mass of the object. The acceleration is The acceleration is equal for all objects ‘g’ ; g = 9.81m/s². !!all objects accelerate !!all objects accelerate at the same rate. Force of Gravity

18. Free Fall Use a=g=10m/s² Example1: Example1: Calculate the force acting on a person jumping from a high rise building (before the parachute opens). The mass of the person is 75kg. The building is 200m high. Example 2: Example 2: What is the mass of a book free falling out of the Saleve 2 nd floor window if the force acting on it is 20N? Example 3: Example 3: What is the force of gravity acting on yourself? Is the force different when you are standing on the ground or jumping from a diving board?

19. Unbalanced Forces In many situations more than one force will be acting on an object. In many situations more than one force will be acting on an object. Engine Force 2000N Road Friction 1500N

20. Free Body Diagrams A free body diagram is a diagram that shows all forces acting on an object. Forces are indicated using arrows: F = 10NF = 5N -The length shows the size of the force. -The arrow points in the direction the force is acting. -The tail shows the point at which the force is acting.(usually centre of gravity of the object)

21. Free Body Diagrams In this case we need to draw a free body diagram of the system In this case we need to draw a free body diagram of the system The arrows are drawn with the length and direction representative of their size. The arrows are drawn with the length and direction representative of their size. The unbalanced force is the sum of these forces. (Note the friction force is in the opposite direction to the engine force so it is a negative number.) The unbalanced force is the sum of these forces. (Note the friction force is in the opposite direction to the engine force so it is a negative number.) The car will accelerate: F=ma The car will accelerate: F=ma a= F/m = 500/1000 = 0.5ms -2 Car Engine Force = 2000NFriction = 1500N Net Force2000 - 1500 = 500N Mass = 1000kg