Teacher’s notes
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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
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Take me straight to the presentation
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.
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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
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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/s2 (that is, metres per second squared). They can also enter their values in both Mega
Newtons and Mega Kilograms to get m/s2 (since the Megas will cancel out).
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Please note that for question 3: 500 kN = 0.5 MN = 500,000 N.
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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.
Newton & The Space Station
After workshop activity
What we are going to do...
• 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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• In the Newton & The Space Station
workshop you discussed movement
and forces on Earth and in space.
Before launch...
Before launch...
What are the
names of forces
A and B?
B
Click here to
reveal the
answers!
A
Before launch...
What are the
names of forces
A and B?
B
A
REACTION FORCE
(Ground pushing back on rocket)
WEIGHT (or GRAVITY)
(Rocket pushing on ground)
Before launch...
B
The rocket is
stationary.
REACTION FORCE
(Ground pushing back on rocket)
Are these forces
balanced or
unbalanced?
Click here to
reveal the
answer!
A
WEIGHT (or GRAVITY)
(Rocket pushing on ground)
Before launch...
B
The rocket is
stationary.
Are these forces
balanced or
unbalanced?
REACTION FORCE
(Ground pushing back on rocket)
The forces are balanced
A
WEIGHT (or GRAVITY)
(Rocket pushing on ground)
Remember...
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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This is Newton’s first law
Launch time!
Launch time!
The rocket generates
thrust and starts to
accelerate.
Are the forces
balanced or
unbalanced?
Click here to
reveal the
answer!
Launch time!
The rocket generates
thrust and starts to
accelerate.
Are the forces
balanced or
unbalanced?
The forces are unbalanced
Launch time!
Thrust = 3.6
Mega Newtons
What is the
resultant force
acting on the
rocket?
Weight = 3.0
Mega Newtons
Click here to
reveal the
answer!
Launch time!
What is the
resultant force
acting on the
rocket?
Thrust = 3.6
Mega Newtons
Resultant force = 0.6
Mega Newtons
Weight = 3.0
Mega Newtons
Remember...
Any resultant
(unbalanced) force
acting on an object will
cause that object to
accelerate (change it’s
motion).
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This is Newton’s second
law
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 law
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)
This is described by this formula:
Force = mass x acceleration
F=ma
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Newton found that the acceleration of an object depends on...
Newton’s second law
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
Force = mass x acceleration
F=ma
MN = Mega Newton
1 MN = 1,000,000 N
Click here to
reveal the
answers!
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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?
Newton’s second law
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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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
Solution to question 4
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/s2
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Size of weight force:
Weight = mass x gravity =
400,000 Kg x 9.8 m/s2
= 3.92 MN
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.
What will happen to the
motion of the rocket?
Click here to
reveal the
answer!
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...
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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This is Newton’s first law
(again!)
During launch...
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!
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...
Any force acting on a
body will experience a
reaction force, of equal
size acting in the
opposite direction.
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This is Newton’s third
law
Newton’s third law
• How many examples can you see in the room
around you?
Click here for
an example!
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• How many examples of action-reaction force
pairs can you think of?
Newton’s third law
Walking: You push on the
floor and the floor pushes
back, making you move!
• How many examples can you see in the room
around you?
Sitting: Your weight pushes
on the chair and the chair
pushes back, so you don’t
fall to the ground!
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• How many examples of action-reaction force
pairs can you think of?
Congratulations!
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• You have completed your
investigation into forces
• What have you learnt today?