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SHM & Energy, Damping

Learning Objectives. Book Reference : Pages 45-46. SHM & Energy, Damping. To be able to answer the question “What is Damping?”. What equipment do cars or bikes tend to have to iron out the bumps in the road?. Questions :.

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SHM & Energy, Damping

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  1. Learning Objectives Book Reference : Pages 45-46 SHM & Energy, Damping To be able to answer the question “What is Damping?”

  2. What equipment do cars or bikes tend to have to iron out the bumps in the road? Questions : • If the car suspension consisted only of springs, what would happen to the motion of the car for sometime after hitting a bump in the road? How would a pendulum continue to swing in an “ideal physics world” with no friction & in a vacuum • What do we observe in the “real-world”

  3. Most vehicles use springs or similar to iron out the lumps and bumps • With only springs the vehicle will continue to bounce (oscillate up and down) for some time after hitting the bump and the passengers would feel sea sick. Think SHM! • Pendulum would keep going with full amplitude for ever • Friction and air resistance reduce the amplitude until eventually the pendulum stops Answers :

  4. Shock absorbers (dampers) Pictures :

  5. Pictures : Shock absorbers (dampers) http://www.acoustics.salford.ac.uk/feschools/waves/shm4.htm

  6. In the “real-world” a system in SHM such as a pendulum or a mass on a spring will eventually come to rest due to “losing energy”, actually doing work against friction and air resistance! Damping

  7. What will the ride in the car be like when • The damping is not strong enough • The damping is too strong • The damping is just right • No bears, kitchen furniture, porridge or small girls with golden hair were harmed in the making of this lesson • [VPL Damping] Damping : The Goldilocks Scenario

  8. Light damping (under damping) • Heavy damping (over damping) • Critical damping Damping : The 3 scenarios

  9. Light damping (under damping) The oscillation slowly dies away (exponential decay). • Heavy damping (over damping) The damping is so strong that the displaced object takes a long time to return to the equilibrium position and does not oscillate • Critical damping : just enough to stop the oscillation as quickly as possible often about T/4 with little or no overshoot Damping : The 3 scenarios

  10. Damping : Many applications What caused this? How could it be avoided?

  11. Caravan Stabiliser : Friction is introduced into the tow mechanism to damp both sideways and up and down motion Damping : Many applications

  12. State is damping is light, critical or heavy in these cases: • A child on a swing, displaced and released • Oil in a U shaped tube displaced from equilibrium and released • What would happen if the oil in a damper (shock absorber) was replaced with very viscous (thick) oil? Problems 1 :

  13. A family car has an unloaded mass of 1000kg. The mass is supported equally by 4 springs. When fully loaded the total mass increases to 1250kg causing the springs to compress by a further 2cm. When the car hits a bump in the road it bounces. Find the period of these oscillations.State assumptions[0.64s] Problems 2:

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