Thanks W Richards-You the man!

1. 06/06/09 Forces and Motion

2. Moments 06/06/09 A moment is a “turning force”, e.g. trying to open or close a door or using a spanner. The size of the moment is given by: Moment (in Nm) = force (in N) x distance from pivot (in m) Calculate the following turning moments: 100 Newtons 5 metres 200 Newtons 2 metres

3. Balancing moments 06/06/09 The anti-clockwise moment is bigger so the seesaw will turn anti-clockwise 100 Newtons 200 Newtons 2 metres 2 metres Total ANTI-CLOCKWISE turning moment = 200x2 = 400Nm Total CLOCKWISE turning moment = 100x2 = 200Nm

4. Balanced or unbalanced? 06/06/09

5. Stability 06/06/09 1. Centre of mass is within the wheelbase – no problem! 2. Centre of mass is directly above the edge of the wheelbase –car is on the point of toppling 3. Car falls over

6. Centripetal force 06/06/09 Consider a ball of Pleistocene attached to some string: The ball is kept in its path by the tension in the string – an example of a CENTRIPETAL FORCE. This force also produces the change in velocity due to the direction constantly changing. This force is INCREASED if you increase the mass of the object, its speed or decrease the radius of the circle. Other examples of centripetal forces: Orbits Electrons

8. Conservation of Momentum 06/06/09 In any collision or explosion momentum is conserved (provided that there are no external forces have an effect). Example question: Two cars are racing around Teville Gate. Car A collides with the back of car B and the cars stick together. What speed do they move at after the collision? Mass = 1000kg Mass = 800kg Momentum before = momentum after… … so 1000 x 50 + 800 x 20 = 1800 x V… … V = 36.7m/s Mass = 1800kg Speed = 50m/s Speed = 20m/s Speed = ??m/s

11. Newton’s Laws of Motion 06/06/09 1) If an unbalanced force acts on an object that object will either accelerate or change direction: 2) That force is given by F=ma 3) When a force acts on an object there is an equal force acting in the opposite direction (“Action and reaction are equal and opposite”) These are my three laws of motion (summarised): F A M

14. Energy loss in collisions 06/06/09 We’ve also said that in a collision momentum is conserved (unless an external force acts). The same cannot usually be said for kinetic energy… For example, consider the following collision. How much kinetic energy is lost? Kinetic energy = ½ x mass x velocity squared in J in kg in m/s In the “Forces” module we looked at how to calculate an object’s kinetic energy: Before After Mass = 1000kg Mass = 800kg Speed = 50m/s Speed = 20m/s Mass = 1000kg Mass = 800kg Speed = 20m/s Speed = 30m/s

15. Energy loss in collisions 06/06/09 Consider a head-on collision where the cars stick together. How much kinetic energy is lost in this example? Where does all the energy go? In this example more kinetic energy was lost. We say it was a “less elastic collision”. An “elastic collision” is one where the kinetic energy is conserved. Before After Speed = 50m/s Speed = 30m/s Speed = 10m/s

16. 06/06/09