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Terminal Velocity

1 September, 2011. Terminal Velocity. Keywords Terminal velocity, Drag, Surface area, Air resistance, Gravity, Acceleration, Weight, Newton’s 2 nd Law. Outcomes. All Must know that: The faster a body moves through a fluid the greater the frictional force which acts on it.

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Terminal Velocity

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  1. 1 September, 2011 Terminal Velocity Keywords Terminal velocity, Drag, Surface area, Air resistance, Gravity, Acceleration, Weight, Newton’s 2nd Law.

  2. Outcomes • All Must know that: The faster a body moves through a fluid the greater the frictional force which acts on it. • Most Will explain what terminal velocity is and be able to use the equation: weight = mass × gravitational field strength. • Some will remember the equation weight = mass × gravitational field strength and see how it links to Newton’s 2nd Law.

  3. Amazing Jump…

  4. Amazing jump • Why do we fall? • Why do we fall at different rates? • How can we change how fast we fall? • Does gravity matter?

  5. Weight Weight = Mass  acceleration due to gravity The force due to gravity depends on the masses of the two objects being attracted to each other. On Earth the force is 10N/kg On the moon it is 1/6th of this – why?

  6. Falling objects. acceleration = 20N/2kg 10m/s2 acceleration = 10N/1kg 10m/s2 ALL OBJECTS FALL AT THE SAME RATE. REALLY? THAT DOESN’T SOUND RIGHT… LET’S PROVE IT. 1kg They fall at the same rate! They both fall at 10m/s2 even though their masses are different! 2kg What rate will they fall? This will be their acceleration. How do we work that out? Force = mass x acceleration So acceleration = Force / mass In our case, acceleration = weight / mass What is the weight? What is the weight? w = m x g w = 1 x 10 = 10N 10N 20N g=10N/kg

  7. But… • This is only true if there are no other forces acting on the object except weight. • What other force is there? • Air Resistance (Drag/Friction)

  8. Falling objects. acceleration ≠ 10N/1kg 10m/s2 It is less acceleration = 10N/1kg 10m/s2 1kg 1kg 1kg Initially forces are unbalanced – Object accelerates in direction of force (down) As the object goes faster it hits intomore air – the air resistance increases – The resultant downward force is less. So it speeds up less quickly – The acceleration decreases. The air resistance increases even moreuntil it is the same as the weight.The resultant = 0N There is no acceleration TERMINAL VELOCITY g=10N/kg

  9. Terminal velocity of a skydiver

  10. Velocity–time graph of skydiver parachute

  11. ball bearing insulating tape viscous fluid Terminal Velocity – Practical Time Results: Aim To observe how objects fallat different rates when droppedthrough different fluids. Set up: We will draw a velocity – time graph for each tube and compare

  12. Copy and Complete (hint – keywords below in blue box): Terminal Velocity As objects move they have………………. When they move ………… they have more air resistance. When the air resistance (and friction) ……….. the force that is pushing them they will go at a constant speed. This is called the ……… ………... Weight is the force on an object due to………... Weight = …………. x gravity. (Gravity = 10m/s2) equals air resistance Terminal Velocitygravity mass quicker 2a) Copy the graph and then explain (i) why a sky diver reaches a maximum speed and (ii) why the maximum speed is a lot lower when the parachute opens. 2b) (i) If the skydiver has a mass of 60kg what will her weight be? Don’t forget to write the units. 2b) (ii) If there is a resultant force of 450N on the skydiver, how long does it take to reach 55.4m/s (124 mph) (Hint – you will need to use F=ma and equation for acceleration)

  13. Outcomes Quiz All : • What happens to the frictional force on the body when it moves through a fluid faster? Most: • What is terminal velocity? • How can I make my terminal velocity increase? • If weight = mass × gravitational field strength, • What is my weight if I am 80Kg? (g=10N/kg) Some: • What is weight? • What is Newton’s 2nd Law?

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