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# Physics in sport 3

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### Physics in sport 3

1. 1. Big Hits! PHYSICS IN SPORT LESSON 3
2. 2. Learning Intentions • Apply Newtons second Law (F=ma) • Know and use the quantity called momentum (p=mv) • Express and use Newtons Second Law in terms of momentum F=Δp/ Δt
3. 3. Newtons First Law • A body will remain at constant speed unless acted on by an unbalanced force • Forces cause changes of velocity. v a t
4. 4. Newtons Second Law • The acceleration of a body is proportional to the force that causes it. • Heavy objects are harder to accelerate than light ones • This is often referred to as inertia F a F  ma But…. Acceleration and therefore force are vector quantities a F
5. 5. Vector form of Newton’s Second Law • We need to ensure we are aware of the direction of our vectors (Which way is +ve?) • A ball (0.5kg) rebounds from a wall at right angles. The impact takes 0.01s. • What is the force acting on the ball? On the wall? 3 ms-1 2 ms-1
6. 6. Vector form of Newton’s Second Law – 2D example • A ball of mass 0.2kg collides with a wall at an angle of 30o. It rebounds at the same angle and the same speed. The impact lasts 0.05s a) Find the average acceleration during impact. b) The force on the ball (and on the wall) 3 ms-1 30o
7. 7. Momentum • Newtons laws were originally expressed in terms of quantity called momentum • Forces caused changes of momentum. • Momentum is the product of an objects mass and velocity p  mv units – kgms-1 v m F  ma mv F t p F t
8. 8. Impulse • Why do you follow through in tennis? • Why do you draw your hands back when you catch a cricket ball • The quantity “force x time” is known as impulse. p F t F  t  p units – Ns 1 Ns = 1 kgms-1
9. 9. Momentum form of Newton’s Second Law • We need to ensure we are aware of the direction of our vectors (Which way is +ve?) • A ball (0.1kg) rebounds from a wall at right angles. The impact takes 0.01s. • What is the force acting on the ball? On the wall? • What is the average acceleration during impact? 2 ms-1 1.5 ms-1
10. 10. A car of mass 1000kg, travels East • A car of mass 1000kg, travels East at 6ms-1 and takes 2 seconds to round a bend, which it does without loss of speed and then heads South. • What average force must turn the car? • What is the radius of the bend?
11. 11. Momentum form of Newton’s Second Law – 2D example • A ball of mass 0.25kg collides with a wall at an angle of 30o. It rebounds at the same angle and the same speed. The impact lasts 0.05s. Find a) The force on the ball (and on the wall). b) the average acceleration during impact 4 ms-1 30o
12. 12. Shunts • A NASCAR coming out of a spin is coasting out of gear at 20 ms-1 when it goes into the path of another car travelling in the same direction at 40 ms-1. When they collide the bumpers lock. How fast do they move after the collision? 20 ms-1 800 kg 40 ms-1 750 kg
13. 13. Slams • Two Hockey players collide • If they hold onto each other after the collision, how do they move? 80 kg 10 ms-1 90 kg 12 ms-1
14. 14. Stones • In curling the players slide 2kg “stones” along the ice toward a target. They score the numbers of stones they have nearest the centre of the target. Collisions to knock out opponents stones are part of the game. • In this shot explore the different scenarios using calculations to justify any conclusions. 8 ms-1 0 ms-1