Transcript PowerPoint file: Higher Physics: Projectiles

What is the connection?
Projectile motion
Which equations can be
used to describe the
motion of projectiles?
What force
acts on an
upward
moving
projectile?
First, think
about…
When the ball is stationary, what forces are
acting on it?
Remove the hands and…?
What happens to the ball?
What
forces are
acting on
the ball?
Air resistance is negligible
Describe the motion using the words velocity,
acceleration and displacement.
Explain in
terms of
forces.
Sketch the velocity–time and acceleration–time
graphs of the motion.
Include values
on the axes.
What force
acts on an
upward
moving
projectile?
Initial vertical
velocity of a
ball dropped
from a
height?
A ball thrown
up in the air.
Vertical
velocity at
maximum
height?
A ball thrown
up in the air.
Is it on its
way up or
down?
For a ball
which is
thrown up
and allowed
to fall back to
exactly the
same point…
…the
downward
motion will
mirror the
upward
motion.
How will
initial vertical
velocity and
final vertical
velocity
compare in
magnitude?
In direction?
Up or down,
what is the
acceleration
of the ball?
–9.8
–2
ms
Remember:
air resistance is
negligible
Describe the
horizontal
motion of this
tennis ball.
Are there
horizontal
forces acting
on the ball?
Does the
horizontal
velocity
change?
Summarise your learning for a
vertical projectile
Direction of
motion
Horizontal
Vertical
Forces
Velocity
Acceleration
Summarise your learning for a
vertical projectile
Direction of
motion
Horizontal
Vertical
Forces
Velocity
Acceleration
Air resistance
negligible so no
forces in the
horizontal
Constant
(in this case
0 m s–1)
None
Air resistance
negligible so only
force of gravity
acting in the
vertical
Changing with
time
Constant or
uniform
acceleration of
– 9.8 m s–2
Another projectile situation…
Picture a motorcyclist…
…on the top of a tall building
about to perform a deathdefying stunt of incredible skill.
DON’T TRY THIS AT HOME
Predict her path once
she launches off the
building.
Predictions for a horizontal projectile
Direction of
motion
Horizontal
Vertical
Forces
Velocity
Acceleration
Just as she
launches…someone
switches off gravity!
Predict her path with
no gravity.
Remember: air
resistance is
negligible.
Switching gravity back on…
Virtual Higher Physics → Mechanics and
Properties of Matter → Projectile Motion
→ Video of projectile motion
(Motion Grapher Simulations:
ball projected horizontally (horizontal
component)
ball projected horizontally (vertical
component))
Summarise your learning for a
horizontal projectile
Direction of
motion
Horizontal
Vertical
Forces
Velocity
Acceleration
Summarise your learning for a
horizontal projectile
Direction of
motion
Horizontal
Vertical
Forces
Velocity
Acceleration
Air resistance
negligible so no
forces in the
horizontal
Constant
None
Air resistance
negligible so only
force of gravity
acting in the
vertical
Changing with
time
Constant or
uniform
acceleration of
– 9.8 m s–2
Class challenge!
Can you save the motorcyclist from
being eaten?
http://www.absorblearning.com/media/attachment.action?quick=ww&att=2357
Do you believe in physics?
Do you trust the equations of
motion?
Would you jump over the
crocodiles based on the
equations?
Verifying the equations of motion
How could you use the equipment to verify the
equations of motion?
Okay then…some hints
What determines the horizontal displacement?
What determines the time spent in the air?
What is the initial vertical velocity of a
horizontal projectile?
Class challenge
Use the
equipment to
determine the
horizontal
velocity with
which the ball
leaves the
launcher.
Safety warnings
(c) Pasco Feedback
Class challenge
How well have you understood?
Calculate the horizontal velocity
required to save the motorcyclist from
being eaten.
http://www.absorblearning.com/media/attachment.action?quick=ww&att=2357
What formula can be used to calculate
the horizontal displacement of an object
fired horizontally if horizontal velocity
and time of flight are known?
horizontal
displacement
(m)
time of flight (s)
sh = uht + ½at2
horizontal
velocity (m s–1)
What formula can be used to calculate
the vertical displacement of an object
fired horizontally?
time of flight (s)
vertical
displacement
(m)
sv = uvt + ½at2
initial vertical
velocity (m s–1)
Which will hit the ground first?
Are the two
balls identical?
Does it matter?
Predict, observe, explain
A thought experiment: the
frictionless marble on the
frictionless surface
The marble is travelling horizontally
at 5 m s–1. Describe its motion at:
0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.6 s,
0.7 s, 0.8 s, 0.9 s, 1.0s
A thought experiment: the
frictionless marble on the
frictionless surface
How can we calculate the horizontal
displacement at:
0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.6 s,
0.7 s, 0.8 s, 0.9 s, 1.0s
The frictionless marble dropped off
the Eiffel Tour (into the airresistance-free Paris sky)
How can we calculate the
vertical displacement at:
0.1 s, 0.2 s, 0.3 s, 0.4 s,
0.5 s, 0.6 s, 0.7 s, 0.8 s,
0.9 s, 1.0s
The frictionless marble:
the complete picture
Using Excel, we can plot a graph of
horizontal displacement against vertical
displacement.
0
0
1
2
3
4
5
6
Vertical displacement (m)
-1
-2
-3
-4
-5
-6
Horizontal displacement (m) Observe and explain
Still don’t believe the
independence of horizontal and
vertical components?
Two more possibilities…
A traditional method involving:
• five small cans, open at each end
• (take care of sharp edges)
• a white board with graph paper (traditional
not
• interactive)
• a method of fixing cans to the board.
• a ball
• a good aim.
Position the cans so the ball, when projected horizontally, will fall
through each can.
A higher technology method
involving:
The photo shown above must have been faked. Explain!
© Pasco Feedback
Group thinking
What do you already
know that you can apply
to projectiles fired at an
angle?
Think forces, vectors,
equations…
© PASCO Feedback
Hints!
Any vector can be
resolved into its
horizontal and vertical
components.
The horizontal component
θ
adjacent
cos  
hypotenuse
adjacent  hypotenuse cos 
horizontal component  launch velocity cos
The vertical component
θ
opposite
sin  
hypotenuse
opposite  hypotenuse sin 
vertical component  launch velocity sin 
Calculate the launch
velocity.
Using this, resolve the
vectors and calculate
the range of the
projectile.
The range is how far
the projectile travels
horizontally.
© PASCO Feedback
From the measured
range, calculated what
the launch velocity
should be.
Are the values the
same?
Explain!
© PASCO Feedback
Predict, then determine
experimentally and by
calculation which angle
will give the greatest
range for a fixed launch
velocity.
© PASCO
Summarise your learning for a
projectile fired at an angle to the
horizontal
Direction of
motion
Horizontal
Vertical
Forces
Velocity
Acceleration
Summarise your learning for a
projectile fired at an angle to the
horizontal
Direction of
motion
Horizontal
Vertical
Forces
Velocity
Acceleration
Air resistance
negligible so no
forces in the
horizontal
Constant
None
Air resistance
negligible so only
force of gravity
acting in the
vertical
Changing with
time
Constant or
uniform
acceleration of
– 9.8 m s–2
Summarise your learning
for all projectiles!
Direction of
motion
Horizontal
Vertical
Forces
Velocity
Acceleration
Projectiles at an angle to the horizontal
http://www.absorblearning.com/media/attachment.action?quick=wx&att=2359
Select a velocity and select an angle.
Calculate the horizontal and vertical components
Will the projectile hit the target?
Other resources
http://www.helpmyphysics.co.uk/projectile.html
http://www.upscale.utoronto.ca/GeneralInterest/Harrison/Flash/Cl
assMechanics/Projectile/Projectile.swf
A thought experiment…
remember our deathdefying motorcyclist?
What would happen if the
building were taller? And the
horizontal velocity greater?
And if the Earth’s surface
curved away more steeply?
This is what Newton thought
about, sometime between 1643
and 1727.
http://www.smaphysics.ca/phys40s/field40s/newtmtn.html
This is taken inside an aircraft. Explain why these NASA trainee
astronauts (class of 2004) appear weightless.
© NASA
Watch the clip on microgravity
http://microgravityuniversity.jsc.nasa.gov/theProgram/video/video
© NAS
Group challenge!
Complete the Weightless Wonder task
to apply your understanding of
equations of motion to a real situation.
http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/Exploring_Space
_Through_Algebra_Weightless_Wonder.html
© NAS
What is gravity?
What is the force of gravity?
What are the effects of gravity?
What do we know about gravity?
How can we make use of gravity?
Investigating the force of gravity on Earth
Using classroom resources, investigate how
you could measure the gravitational field
strength on Earth.
What are you measuring?
How are you measuring it?
What does it mean?
© NASA
Uncertainties in your results
© NASA
What do the results mean?
What have you measured?
© NASA
Can you measure gravitational
field strength directly?
© NASA
Making use of the force of gravity
Newton’s thought experiment of 300 years ago
became a reality on 4 October 1957.
The Soviet Union (USSR) successfully
launched the world’s first artificial satellite,
Sputnik 1.
http://history.nasa.gov/sputnik/sputnik.wav
Researching physics
What was the significance of Sputnik’s launch,
more than 50 years ago?
What impact has the space race and our ability
to launch satellites into space had on life on
Earth?
Topics for researching
• The historical aspects of the space race and
its significance to humankind.
• Low orbit and geostationary satellites.
• Satellite communication and surveying.
• Environmental monitoring of the conditions
of the atmosphere.
Scientific communication and
criteria for assessment
Another opportunity to build skills for
researching physics units.
Insert more information once released!
Quality sources for research.
Communication of understanding, including
summarising information in own words.
Scientific content within communication.
Reviewing our learning
In this section, we have developed our
understanding of motion to build from vertical
projectiles, to horizontal projectiles and projectiles at
an angle.
We have followed the thought processes of Sir
Isaac Newton through to the very first successful
launch of a satellite, and considered how scientific
developments impact on life on Earth.
A final thought…
This paragraph is taken from an article about a
sample of wood being taken on a NASA
mission to orbit Earth.
A piece of Sir Isaac Newton's apple tree will
‘defy’ gravity, the theory it inspired, when
it is carried into space on the next Nasa
shuttle mission. © BBC News website
Discuss!