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Forces Forces After workshop After workshop activity activity
ForcesForcesAfter workshop After workshop
activityactivity
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.
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Before launch...
AA
BB
Before launch...
What are the names of forces
A and B?
Click here to reveal the answers!
AA
BB
Before launch...
What are the names of forces
A and B?
WEIGHTWEIGHT (or (or GRAVITYGRAVITY))(Rocket pushing on ground)(Rocket pushing on ground)
REACTION FORCEREACTION FORCE(Ground pushing back on rocket)(Ground pushing back on rocket)
AA
BB
Before launch...
The rocket is stationary.
Are these forces balanced or unbalanced?
WEIGHTWEIGHT (or (or GRAVITYGRAVITY))(Rocket pushing on ground)(Rocket pushing on ground)
REACTION FORCEREACTION FORCE(Ground pushing back on rocket)(Ground pushing back on rocket)
Click here to reveal the answer!
AA
BB
Before launch...
The rocket is stationary.
Are these forces balanced or unbalanced?
WEIGHTWEIGHT (or (or GRAVITYGRAVITY))(Rocket pushing on ground)(Rocket pushing on ground)
REACTION FORCEREACTION FORCE(Ground pushing back on rocket)(Ground pushing back on rocket)
The forces are balanced
Remember...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.
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Launch time!
Launch time!
Click here to reveal the answer!
The rocket generates thrust and starts to accelerate.
Are the forces balanced or unbalanced?
Launch time! The rocket generates thrust and starts to accelerate.
Are the forces balanced or unbalanced?
The forces are unbalanced
Launch time!
What is the resultant force acting on the
rocket?
Click here to reveal the answer!
Weight = 3.0 Weight = 3.0 Mega NewtonsMega Newtons
Thrust = 3.6 Thrust = 3.6 Mega NewtonsMega Newtons
Launch time!
What is the resultant force acting on the
rocket?
Weight = 3.0 Weight = 3.0 Mega NewtonsMega Newtons
Thrust = 3.6 Thrust = 3.6 Mega NewtonsMega Newtons
Resultant force = 0.6 Resultant force = 0.6 Mega NewtonsMega Newtons
Remember...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).
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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!
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
This is also Newton’s second lawThis 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)
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This is described by this formula:
Force = mass x acceleration
F = m a
Newton’s second lawNewton’s second law1. 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
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Force = mass x acceleration
F = m a
MN = Mega Newton1 MN = 1,000,000 N
Click here to reveal the answers!
Newton’s second lawNewton’s second law1. 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/s2
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/s2
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 13.95 m/s2
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During launch...
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.
Click here to reveal the answer!
What will happen to the motion of the rocket?
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
Remember...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.
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During launch...
During launch...
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?
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!
Remember...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.
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Newton’s third lawNewton’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?
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Click here for an example!
Newton’s third lawNewton’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?
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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!
Congratulations!Jodrell Bank D
iscovery Centre• You have completed your
investigation into forces
• What have you learnt today?
