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This lesson

This lesson. Know what a force is Types of force Vectors and scalars Newton’s Laws. Forces. Remember a force is a push (or pull). Forces. Force is measured in Newtons. Forces. There are many types of forces; electrostatic, magnetic, upthrust, friction, gravitational……….

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This lesson

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  1. This lesson • Know what a force is • Types of force • Vectors and scalars • Newton’s Laws

  2. Forces • Remember a force is a push (or pull)

  3. Forces • Force is measured in Newtons

  4. Forces • There are many types of forces; electrostatic, magnetic, upthrust, friction, gravitational………

  5. Friction opposes motion!

  6. Newton’s Laws of Motion That’s me!

  7. Newton’s 1st Law If there is no resultant force acting on an object, it will move with constant velocity. (Note the constant velocity could be zero).

  8. Newton’s 1st Law Does this make sense? If there is no resultant force acting on an object, it will move with constant velocity. (Note the constant velocity could be zero).

  9. Newton’s 1st Law Can you copy it whilst you think about it? If there is no resultant force acting on an object, it will move with constant velocity. (Note the constant velocity could be zero).

  10. Newton’s 1st law Newton’s first law was actually discovered by Galileo. Newton nicked it!

  11. Newton’s first law Galileo imagined a marble rolling in a very smooth (i.e. no friction) bowl.

  12. Newton’s first law If you let go of the ball, it always rolls up the opposite side until it reaches its original height (this actually comes from the conservation of energy).

  13. Newton’s first law No matter how long the bowl, this always happens

  14. Newton’s first law No matter how long the bowl, this always happens. constant velocity

  15. Newton’s first law Galileo imagined an infinitely long bowl where the ball never reaches the other side!

  16. Newton’s first law The ball travels with constant velocityuntil its reaches the other side (which it never does!). Galileo realised that this was the natural state of objects when no (resultant ) forces act. constant velocity

  17. Another example Imagine Mr Porter cycling at constant velocity.

  18. Newton’s 1st law He is providing a pushing force. Constant velocity

  19. Newton’s 1st law There is an equal and opposite friction force. Pushing force friction Constant velocity

  20. Let’s watch a video.... • http://www.youtube.com/watch?v=Q0Wz5P0JdeU

  21. Newton’s second law Newton’s second law concerns examples where there is a resultant force. I thought of this law myself!

  22. Let’s go back to Mr Porter on his bike. Remember when the forces are balanced (no resultant force) he travels at constant velocity. Pushing force friction Constant velocity

  23. Newton’s 2nd law Now lets imagine what happens if he pedals faster. Pushing force friction

  24. Newton’s 2nd law His velocity changes (goes faster). He accelerates! Remember that acceleration is rate of change of velocity. In other words acceleration = (change in velocity)/time Pushing force friction acceleration

  25. Newton’s 2nd law Now imagine what happens if he stops pedalling. friction

  26. Newton’s 2nd law He slows down (decellerates). This is a negative acceleration. friction

  27. Newton’s 2nd law So when there is a resultant force, an object accelerates (changes velocity) Mr Porter’s Porche Pushing force friction

  28. Newton’s 2nd law There is a mathematical relationship between the resultant force and acceleration. Resultant force (N) = mass (kg) x acceleration (m/s2) It’s physics, there’s always a mathematical relationship! FR = ma

  29. Newton’s 2nd law There is a mathematical relationship between the resultant force and acceleration. Resultant force (N) = mass (kg) x acceleration (m/s2) Can you copy this too? FR = ma

  30. An example What will be Mr Porter’s acceleration? Mass of Mr Porter and bike = 100 kg Pushing force (100 N) Friction (60 N)

  31. An example Resultant force = 100 – 60 = 40 N FR = ma 40 = 100a a = 0.4 m/s2 Mass of Mr Porter and bike = 100 kg Pushing force (100 N) Friction (60 N)

  32. Let’s watch a video... • http://www.youtube.com/watch?v=WzvhuQ5RWJE&feature=related

  33. Newton’s 3rd law If a body A exerts a force on body B, body B will exert an equal but opposite force on body A. Hand (body A) exerts force on table (body B) Table (body B) exerts force on hand (body A)

  34. Let’s watch a video... • http://www.youtube.com/watch?v=cP0Bb3WXJ_k&feature=related

  35. Don’t worry! We won’t really do Newton’s 3rd law until year 12!

  36. That’s all folks!

  37. Let’s try some questions! He promised us it would stop…..

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