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Teacher’s notes This is an interactive presentation for use after pupils have experienced the Newton & The Space Station workshop. It follows the various stages of a rocket launch and is designed to consolidate pupils’ learning on Newton's three laws of motion. Objectives –To interpret the motion of a rocket during launch. –To identify balanced and unbalanced forces. –To calculate and interpret the acceleration of a rocket. –To analyse and discuss action-reaction force pairs. Note on using this presentation: when a question is asked, it is only possible to move to the next slide by clicking the green square on the slide, or using the cursor buttons on the keyboard. Clicking outside the green square will not advance the slide. It is up to teachers how pupils answer the questions. Some teachers may prefer group discussions followed by verbal feedback, whilst others may wish their students to answer on mini-whiteboards, for example. Slide 19 The questions on slide 19 are mathematical in nature and pupils will need a calculator to complete these. Pupils are required to rearrange the equation F=ma to a = F/m for some of these questions. If pupils enter their values in Newtons and Kilograms, their answers will be in the correct unit of acceleration, m/s 2 (that is, metres per second squared). They can also enter their values in both Mega Newtons and Mega Kilograms to get m/s 2 (since the Megas will cancel out). Please note that for question 3: 500 kN = 0.5 MN = 500,000 N. Question 4 requires that the resultant force on the rocket be calculated afresh. Assuming that the rocket is travelling straight up, there are two forces acting downwards: air resistance and the rocket’s weight. Both these forces counteract the upwards thrust force of the rocket. A solution is presented on slide 20. Take me straight to the presentation

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Newton & The Space Station After workshop activity

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What we are going to do... In the Newton & The Space Station 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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Before launch...

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

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

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

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

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Remember... This is Newton’s first law 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

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Launch time!

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

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

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

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

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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

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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!

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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

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This is also Newton’s second law Newton found that the acceleration of an object depends on... 1.The size of the force (a bigger force produces a bigger acceleration) 2.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

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Newton’s second law 1. 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? 2. The mass of the Arianne 5 rocket is 777,000 Kg. What is the acceleration of the rocket? 3. 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) 4. [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 Force = mass x acceleration F = m a MN = Mega Newton 1 MN = 1,000,000 N Click here to reveal the answers!

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Newton’s second law 1. 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 2. The mass of the Arianne 5 rocket is 777,000 Kg. What is the acceleration of the rocket? 7.6 m/s 2 3. 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/s 2 4. [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/Kg13.95 m/s 2 Jodrell Bank Discovery Centre

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Solution to question 4 Jodrell Bank Discovery Centre Size of weight force: Weight = mass x gravity = 400,000 Kg x 9.8 m/s 2 = 3.92 MN Size of resultant force on rocket: F = 13.5 MN – 4 MN – 3.92 MN = 5.58 MN Acceleration of rocket: a = F / M = 5,580,000 N / 400,000 Kg = 13.95 m/s 2

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During launch...

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

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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

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Remember... This is Newton’s first law (again!) 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

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During launch...

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

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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!

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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

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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!

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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 Walking: You push on the floor and the floor pushes back, making you move! Sitting: Your weight pushes on the chair and the chair pushes back, so you don’t fall to the ground!

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

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