Centre of Gravity
•
Learning Objective: Apply knowledge of
centres of gravity with free-body force
diagrams
The big questions:
- What is a centre of gravity and a free-body
force diagram
- How do we find the centre of gravity
- How can I work out forces for a free-body
force diagram
Why does the plane fall?
http://www.youtube.com/watch?v=Y5ZqXYt5
-qA&feature=related
Gravity
E – Pick a normal object (square, circle,
triangle etc) and label its centre of gravity
and gravity force
D – Draw a globe and a normal object with its
centre of gravity and gravity force
C – Draw a globe with 4 normal objects and
their centre and gravity forces
Centre of Gravity
•
Learning Objective: Apply knowledge of
centres of gravity with free-body force
diagrams
The big questions:
- What is a centre of gravity and a free-body
force diagram
- How do we find the centre of gravity
- How can I work out forces for a free-body
force diagram
Quick steps to find centre of gravity of an
irregular object…
Hang it from a point using string
Draw a line down from the string
through the object
Hang it from a different point
Draw another line down, where the lines meet
is where the centre of gravity is
EXT Q: Why does the object stay still?
Centre of Gravity
•
Learning Objective: Apply knowledge of
centres of gravity with free-body force
diagrams
The big questions:
- What is a centre of gravity and a free-body
force diagram
- How do we find the centre of gravity
- How can I work out forces for a free-body
force diagram
A free body force diagram is one with ALL
forces.
E – Draw all forces as arrows
C - Label all forces on diagrams, including
those on a slope (‘gravity’, ‘friction’ etc)
A – When labelling diagrams label ‘the object
pulling the earth’, and split up diagonal
forces
Answer the ‘big questions’ as
you go around the room
•
Learning Objective: Apply knowledge of
centres of gravity with free-body force
diagrams
The big questions:
- What is a centre of gravity and a free-body
force diagram
- How do we find the centre of gravity
- How can I work out forces for a free-body
force diagram
SOH CAH TOAAAAA
•
Learning Objective: Link trigonometry to
force diagrams
The big questions:
- Can you draw a force diagram for any object
- Can you use soh cah toa
- Are you able to link soh cah toa to forces at
an angle?
Throw the fruit…
Why are some fruits going further?
On the A3 paper draw each fruit with its
forces including the throwing force
Ext: Draw a skier going down a slope
As a group complete the SOH CAH TOA
worksheet
SOH CAH TOAAAAA
•
Learning Objective: Link trigonometry to
force diagrams
The big questions:
- Can you draw a force diagram for any object
- Can you use soh cah toa
- Are you able to link soh cah toa to forces at
an angle?
Spotlight time…
2 minutes to answer the question, then
one is chosen to present your work and
everybody else votes if they were doing it
correctly
Q: A man is pulled out of a window
by a force of 10 N horizontally
and 5 N vertically.
What angle does he get thrown out at?
(remember there will be two answers)
SOH CAH TOAAAAA
•
Learning Objective: Link trigonometry to
force diagrams
The big questions:
- Can you draw a force diagram for any object
- Can you use soh cah toa
- Are you able to link soh cah toa to forces at
an angle?
Questions from past papers:
Jan ‘10 q5, q16,
Jan ‘11 q4, q16
(on board)
What angle and force are created if a
football is kicked by two players at once:
One player kicking it left with 40N and
one kicking up with 20N?
EXT: What if one kicked it left with 40N
and one kicked it right with 30N?
SOH CAH TOAAAAA
•
Learning Objective: Link trigonometry to
force diagrams
The big questions:
- Can you draw a force diagram for any object
- Can you use soh cah toa
- Are you able to link soh cah toa to forces at
an angle?
Easiest big question?
Hardest big question
Write a learning objective for the lesson
as a whole
Things Mr. Harrison did that made this
easier were….
Things Mr. Harrison could do to make it
even easier would be ……