KICKSTART PHYSICS
SPACE
1. SPEED AND ESCAPE VELOCITY
2. PROJECTILE MOTION
3. ACCELERATION AND G-FORCES
4. ‘C’ AND RELATIVITY
5. EINSTEIN
Kickstart would like to acknowledge and pay respect to the traditional owners of the land – the
Gadigal people of the Eora Nation. It is upon their ancestral lands that the University of Sydney is built.
As we share our knowledge, teaching, learning, and research practices within this University may we
also pay respect to the knowledge embedded forever within the Aboriginal Custodianship of Country.
For more information head to
http://sydney.edu.au/science/outreach/high-school/kickstart/index.shtml
The University of Sydney
School of Physics
Space
Get to Know the Inner Space
Risk Analysis
Conduct a risk analysis by filling out the following table.
List 3 risks to do with this investigation in the 2nd year lab. Also, list 3 risks in an industry where physics is used.
− What are the consequences of those risks? Use the risk matrix below to make your judgment.
− What precautions would you take to stop those risks from coming about?
− What steps would you take to mitigate those risks?
Risk
Consequence
Precaution/Mitigation
Kickstart
Electricity
Radiation
Equipment
Water
LN2
Electrocution (High)
Radiation Sickness (High)
Tripping and Injury (Medium)
Slipping and Injury (Medium)
Frostbite (High)
Safety Switch
Low Dose/Shielding
Don’t Touch
No Food/Drink in Lab
Personal Protective Equipment
Physics
Industry
Industry – Finance/Tech,
Games, Solar Power, Medical
Physics, Radiology
Research – University,
Academia
Public Service – CSIRO, DSTO,
NMI, Questacon, Government,
Teachers
See above, jobs might require
more specific considerations
See above, jobs will require
more specific considerations
What sort of careers do you think you could get if you studied this topic at the University of Sydney?
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The University of Sydney
School of Physics
Space
Speed & Escape Velocity
There are a number of different types of orbits in orbital systems.
Model each of the following orbits with the gravity trampoline, and identify what object might have that
orbit.
Type of Orbit
How to Model the Orbit
Examples of Objects with the Orbit
Highly Eccentric Orbit
Give the object a push, but not strong
enough to dislodge it from making a
complete orbit
Halley’s Comet
Hyperbolic Orbit
Give the object a strong push to prevent
it from continuing orbit
Asteroid
Orbital Decay
Start the orbit with a slight push so that it
decays towards the centre
International Space Station, LEO
After modeling Low Earth and Geostationary Orbits on the gravity trampoline, compare the two by listing
their similarities and differences.
Similarities
Differences
- Earth orbits
- Remote sensing
- Used for communications
- Sees different parts of the Earth
-
- Different orbital speeds
-
- Different purposes
We can use energy and force to determine the velocity of objects as they leave the planet and into orbit.
Escape Velocity
The kinetic energy of an object with mass m is given by:
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𝐸! = 𝑚𝑣 !
2
The gravitational potential energy of an object with mass m in the gravitational field of an object with mass
M is given by:
𝐺𝑚𝑀
𝐸! = −
𝑟
Derive a formula for the escape velocity:
𝐸!! + 𝐸!! = 𝐸!! + 𝐸!! ⟹ since final kinetic and potential energies are 0
1
𝐺𝑚𝑀
∴ 𝑚𝑣 ! −
=0
2
𝑟
1
𝐺𝑚𝑀
2𝐺𝑀
𝑚𝑣 ! =
⟹ 𝑣! =
2
𝑟
𝑟
∴𝑣=!
2𝐺𝑀
𝑟
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The University of Sydney
School of Physics
Space
Orbital Velocity
The equation for the force acting on an object with mass m and velocity v in a circular path of radius r is
given by: (the centripetal force)
𝑚𝑣 !
𝐹=
𝑟
The equation for the gravitational force between two objects with masses m1 and m2 is given by:
𝐺𝑚! 𝑚!
𝐹=
𝑟!
Derive a formula for the orbital velocity:
Since gravitational and centripetal force are pointed in the same direction, they are equal:
𝑚𝑣 ! 𝐺𝑚𝑀
=
𝑟
𝑟!
𝐺𝑀
𝑣! =
𝑟
∴𝑣=!
𝐺𝑀
𝑟
What do these formulae say about the concepts of escape and orbital velocity?
For either orbital velocity or escape velocity, we do not need to consider the mass of the object we are
concerned with; it is not a variable!
Kepler’s Laws
Kepler’s three laws of planetary motion describe the motion of orbiting bodies. They are:
1. The orbit of every planet is an ellipse with the Sun at one of the two foci.
2. A line joining a planet and the Sun sweeps out equal areas during equal intervals of time:
3. 𝑇 ! ∝ 𝑅 !
Use the gravity trampoline to help demonstrate each of Kepler’s three laws of planetary motion.
How would you derive Kepler’s 3rd Law from the orbital velocity of an object in orbit?
velocity = distance 2𝜋𝑟
=
time
𝑇
2𝜋𝑟 𝐺𝑀
4𝜋 ! 𝑟 ! 𝐺𝑀
!
Substituting into our orbital velocity equation, =
⟹
=
𝑇
𝑟
𝑇!
𝑟
Simplication and rearrangement gives us:
𝑟!
𝐺𝑀
=
-­‐ that is, Kepler's Third Law!
!
𝑇
4𝜋 !
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The University of Sydney
School of Physics
Space
Projectile Motion
Monkey and the Hunter
Predict
Above:
Below:
At:
Students make predictions
Students make predictions
Students make predictions
Observe
Explain
Miss
In projectile motion, gravity is
acting on both of the object’s
vertical velocities, but not on it’s
horizontal motion.
Miss
In projectile motion, gravity is
acting on both of the object’s
vertical velocities, but not on it’s
horizontal motion.
Hit
In projectile motion, gravity is
acting on both of the object’s
vertical velocities, but not on it’s
horizontal motion.
This process of Predict, Observe, Explain, Apply was used by
David Unaipon (1872-1967), known as “Australia’s Leonardo
Da Vinci”. He was of the Ngarrindjeri people of South Australia
and was an Aboriginal inventor and author who made
significant contributions to science.
David invented many devices, including a sheep shearer that is
still in use today. He never received any recognition or
monetary benefit from any of his innovative inventions.
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The University of Sydney
School of Physics
Space
Acceleration & G-Forces
Acceleration
Describe how you moved for each of the graphs that
you matched:
Position vs Time
Velocity vs Time
Acceleration vs Time
Features
Straight lines correspond to
constant velocity; there can
be positive and negative
directions.
Horizontal lines correspond
to constant acceleration.
Positive and negative values
for acceleration are
observed.
Characteristics
Move forward and back.
Move forward and back.
Move forward and back.
Where would you experience the highest and lowest g-force?
Highest = where acceleration is greatest and acting against gravity, lowest = where acceleration is greatest
and acting with gravity.
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The University of Sydney
School of Physics
Space
‘C’ & Relativity
The Michelson-Morley Interferometer
Observe the interference pattern as you change the path
length for one of the light beams by carefully adjusting
the position of the moveable mirror. What happens to the
pattern?
Sketch the interference pattern you see through the view piece:
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The University of Sydney
School of Physics
Space
A Slower Speed of Light
Relativity is a very difficult thing to study. This is why we use models and visualisations.
With the game “A Slower Speed of Light” you can qualitatively describe some effects of relativity.
However, with all models, there are limitations and inaccuracies. Sometimes, the use of a model can actually
have a negative effect on the intended purpose of the model.
In the following table, list some limitations and inaccuracies to this model:
Advantages
Limitations
Can visualise effects of speed of light travel
Not the full story
Easy to understand demo of effects
Much more complicated than presented
Can get some quantitative and qualitative data
Inaccuracies and misconceptions can arise from the
model
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The University of Sydney
School of Physics
Space
Einstein
An hour sitting with a pretty girl on a
park bench passes like a minute, but a
minute sitting on a hot stove seems like an
hour.
- Albert Einstein
Using the equation for time dilation:
𝑡
𝑡! =
1−
𝑣!
𝑐!
fill in the table for the effect of time dilation in days and years with respect to the percentage of the speed
of light.
Speed (% of c)
Days
Years
0
1
0.003
50
1.15
0.003
90
2.29
0.006
99.5
31.6
0.02
99.999999999
223606
612
What is the time dilation experienced by astronauts on the International Space Station from the reference
frame of people on the surface of the Earth? The orbital speed of the ISS is 7.66 kms-1.
𝑡! =
1
!
!1 − 7666.67
!
𝑐
= 1.01 days = 0.003 years
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The University of Sydney
School of Physics
Space
Inertial Frames of Reference vs Non-Inertial Frames of Reference
Inertial Frame of Reference: The frame of reference where the Newtownian concept of inertia holds.
Non-Inertial Frame of Reference: The frame of reference where the Newtownian concept of inertia does not
hold.
How can we distinguish between the two?
The easiest way to illustrate this difference is with rotating reference frames. Why is that?
Use the graph paper to illustrate the difference between inertial and non-inertial reference frames:
Inertial Frame
Non-Inertial Frame
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