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Forces

Forces. After workshop activity. What we are going to do. In the Forces workshop you discussed movement and forces on Earth and in space. We are going to look at the forces at different stages of a rocket launch to see how much you have learnt. Jodrell Bank Discovery Centre.

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Forces

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  1. Forces After workshop activity

  2. What we are going to do... • In the Forces workshop you discussed movement and forces on Earth and in space. • We are going to look at the forces at different stages of a rocket launch to see how much you have learnt. Jodrell Bank Discovery Centre

  3. Before launch...

  4. Before launch... B What are the names of forces A and B? Click here to reveal the answers! A

  5. Before launch... REACTION FORCE (Ground pushing back on rocket) B What are the names of forces A and B? WEIGHT(or GRAVITY) (Rocket pushing on ground) A

  6. Before launch... REACTION FORCE (Ground pushing back on rocket) B The rocket is stationary. Are these forces balanced or unbalanced? Click here to reveal the answer! WEIGHT(or GRAVITY) (Rocket pushing on ground) A

  7. Before launch... REACTION FORCE (Ground pushing back on rocket) B The rocket is stationary. Are these forces balanced or unbalanced? The forces are balanced WEIGHT(or GRAVITY) (Rocket pushing on ground) A

  8. Remember... This is Newton’s first law (part 1) If the forces on a stationary object are balanced, the object will remain stationary until an unbalanced force acts upon it. Jodrell Bank Discovery Centre

  9. Launch time!

  10. Launch time! The rocket generates thrust and starts to accelerate. Are the forces balanced or unbalanced? Click here to reveal the answer!

  11. Launch time! The rocket generates thrust and starts to accelerate. Are the forces balanced or unbalanced? The forces are unbalanced

  12. Thrust = 3.6 Mega Newtons Launch time! What is the resultant force acting on the rocket? Weight = 3.0 Mega Newtons Click here to reveal the answer!

  13. Thrust = 3.6 Mega Newtons Launch time! What is the resultant force acting on the rocket? Resultant force = 0.6 Mega Newtons Weight = 3.0 Mega Newtons

  14. Remember... This is Newton’s second law Any resultant (unbalanced) force acting on an object will cause that object to accelerate (change it’s motion). Jodrell Bank Discovery Centre

  15. Launch time! As the rocket lifts up, fuel gets used. How does this affect the acceleration of the rocket? Click here to reveal the answer!

  16. Launch time! As the rocket lifts up, fuel gets used. How does this affect the acceleration of the rocket? As the rocket loses mass, the acceleration increases

  17. This is also Newton’s second law Newton found that the acceleration of an object depends on... • The size of the force (a bigger force produces a bigger acceleration) • The mass of the object (a bigger mass results in a smaller acceleration) Jodrell Bank Discovery Centre This is described by this formula: Force = mass x acceleration F = m a

  18. Newton’s second law • An Arianne 5 rocket can produce 13.5 MN of thrust, but has a weight of 7.6 MN. What is the resultant force at launch? • The mass of the Arianne 5 rocket is 777,000 Kg. What is the acceleration of the rocket? • The force of air resistance increases as the rocket speed increases. Five seconds into flight the air resistance is 500 KN. What is the new acceleration of the rocket? (assume a constant thrust and mass) • [Harder] As the rocket travels, it uses fuel and its mass decreases. Five minutes into flight the mass of the rocket has reduced to 400,000 Kg, but the air resistance has increased to 4 MN. What is the new acceleration of the rocket? (assume a constant thrust) Hint: The weight of the rocket has changed. Weight = mass x gravity. Gravity on Earth = 9.8 N/Kg Jodrell Bank Discovery Centre Click here to reveal the answers! Force = mass x acceleration F = m a MN = Mega Newton 1 MN = 1,000,000 N

  19. Newton’s second law • An Arianne 5 rocket can produce 13.5 MN of thrust, but has a weight of 7.6 MN. What is the resultant force at launch? 5.9 Mega Newtons • The mass of the Arianne 5 rocket is 777,000 Kg. What is the acceleration of the rocket? 7.6 m/s2 • The force of air resistance increases as the rocket speed increases. Five seconds into flight the air resistance is 500 KN. What is the new acceleration of the rocket? (assume a constant thrust and mass) 6.9 m/s2 • [Harder] As the rocket travels, it uses fuel and its mass decreases. Five minutes into flight the mass of the rocket has reduced to 400,000 Kg, but the air resistance has increased to 4 MN. What is the new acceleration of the rocket? (assume a constant thrust) Hint: The weight of the rocket has changed. Weight = mass x gravity. Gravity on Earth = 9.8 N/Kg 13.95 m/s2 Jodrell Bank Discovery Centre

  20. During launch...

  21. During launch... As the speed of the rocket increases, the force of air resistance increases. Eventually, the air resistance force balances with the thrust force. What will happen to the motion of the rocket? Click here to reveal the answer!

  22. During launch... As the speed of the rocket increases, the force of air resistance increases. Eventually, the air resistance force balances with the thrust force. What will happen to the motion of the rocket? The rocket will continue to move, in a straight line at a constant speed

  23. Remember... This is Newton’s first law (part 2) If the forces on a moving object are balanced, the object will continue moving at a constant speed in a straight line, until an unbalanced force acts upon it. Jodrell Bank Discovery Centre

  24. During launch...

  25. During launch... How does the rocket generate thrust? Remember the two volunteers on the trolleys, with the rope? How did this explain a rocket launching? Click here to reveal the answer!

  26. During launch... How does the rocket generate thrust? The rocket pushes on the exhaust gas; forcing it out. The gas pushes back on the rocket, producing an upwards thrust!

  27. Remember... This is Newton’s third law Any force acting on a body will experience a reaction force, of equal size acting in the opposite direction. Jodrell Bank Discovery Centre

  28. Newton’s third law • How many examples of action-reaction force pairs can you think of? • How many examples can you see in the room around you? Jodrell Bank Discovery Centre Click here for an example!

  29. Newton’s third law • How many examples of action-reaction force pairs can you think of? • How many examples can you see in the room around you? Walking: You push on the floor and the floor pushes back, making you move! Jodrell Bank Discovery Centre Sitting: Your weight pushes on the chair and the chair pushes back, so you don’t fall to the ground!

  30. Congratulations! • You have completed your investigation into forces • What have you learnt today? Jodrell Bank Discovery Centre

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