Learning Objectives:

1
Learning Objectives

• To recap knowledge of basic forces.
• To understand that forces can produce turning
  effects.
• To know how to calculate moments.
• To be able to give situations where turning
  forces are useful.

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Forces
3
Recap

• AQA Physics Page 212.
• Read the page and answer recap questions 1 4.

4
Turning Forces

• As well as causing translational movement forces
  can make things turn.
• We often use turning forces in simple leavers.

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Turning Forces
6
Wait a Moment!

• The turning effect of a force is called a moment.
• How can we make the turning effect of a force
  bigger?

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Moments

• The turning effect of a force can be made larger
  by
• Increasing the size of the applied force.
• Increasing the distance away from the pivot
  where the force is applied.

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Moments

• Moment (Nm) Force (N) x Perpendicular distance
• from pivot (m)
• Where can the largest load be placed on the crane?

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Moments
10
Moments

• If an object is in equilibrium (i.e. the forces
  on it are all balanced and it doesnt move) then
  the clockwise moments equal the anticlockwise
  moments.

11
Thought Experiments

• Why when cutting card with scissors do we cut
  near the pivot?
• How do wheel barrows help us lift heavy loads?

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Summary

• Read pages 214 215 and 218 219 of the text
  book in silence.
• Complete the summary questions and copy the key
  points on each of the pages.

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Centre of Mass

• The centre of mass of an object is the point on
  the object where all its mass may be thought to
  be concentrated,

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Moments Questions

• Read AQA Physics Page 218 219.
• Complete Summary Questions 1 and 2.
• Make a neat copy of figure 4
• Using Moments
• Copy Key Point

15
Learning Objectives

• To understand what makes objects stable.
• To be able to determine when an object will
  topple over.
• To be able to design a stable object.

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Stability
http//www.youtube.com/watch?v2tlcDTByGygfeature
related
17
Stability

• Objects will not topple over if their centre of
  mass falls within their base.
• So how can we make objects more stable?

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Which glass?
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Stability

• Prove that a brick falls over when the centre of
  mass is outside its base.
• Draw diagonal lines corner to corner across the
  long flat side of the brick assuming it is
  uniform where they meet is the centre of mass.
• Use a clamp stand to show you the vertical
  (similar to using a plumb line last lesson).
• Slowly tilt the brick, the brick should only
  topple over when the centre of mass no longer
  falls inside the base, i.e. the diagonal line
  you have drawn goes past the vertical.

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Stability

• Draw the design for a vase that would be very
  stable, but would still hold a tall bunch of
  flowers.

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Stability Activities

• Read AQA Physics Page 220 - 221.
• Complete Summary Questions 1 and 2.
• Make a neat copy of figure 1
• tilting and Toppling
• Copy Key Points

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Starter Questions

• Work out the missing force in each picture if the
  beams are in equilibrium.

0.8 m
0.3 m
? N
12 N
? N
0.8 m
0.4 m
0.3 m
12 N
18 N
23
Learning Objectives

• To know the name for the force that causes
  objects to move in a circle.
• To know the factors that affect the size of this
  force.
• To understand that objects moving in a circle are
  constantly accelerating.

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Circular Motion

• http//uk.youtube.com/watch?v-G7tjiMNVlc

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Circular Motion

• Circular motion occurs when a resultant force
  towards the centre of the circle acts on an
  object. This resultant force is called the
  centripetal force.

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Circular Motion

• What causes the centripetal force in each of
  these situations?

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Circular Motion

• What happens if the centripetal force is removed?
• If the centripetal force is removed the object
  will move off at a tangent to the circle.

28
Circular Motion

• As the object changes direction when it moves
  around the circle, its velocity must be changing.
  Acceleration is a change in velocity, so the
  object is always accelerating towards the centre
  of the circle.

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Circular Motion

• If centripetal force acts towards the middle of
  the circle, why do you get pushed outwards when a
  car goes round a corner?
• You dont really get pushed outwards. You
  continue to move forwards, as the centripetal
  force tries to pull you around the corner. The
  faster your moving the greater your inertia
  (resistance to a change in speed) and the greater
  the force you feel.

30
Circular Motion

• What affects the size of the centripetal force
  needed to keep an object moving in a circle?
• The faster an object the larger the force
  needed.
• The more massive an object the larger the force
  needed.
• The smaller the radius of the circle the larger
  the force needed.

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Circular Motion Activities

• AQA Physics Page 222 223 Read the pages
  carefully.
• Copy the key points.
• Answer questions 1 and 2, copying the diagram
  out for question 1.

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Home Work

• Produce a report on at least one side of A4 on
  satellites. Include information on satellites
  stay in orbit, the different types of orbit and
  types of satellite. The work must be hand
  written, but should include printed pictures.

33
Starter Questions

• Work out the missing distances in each picture if
  the beams are in equilibrium.

2.80 m
? m
20 N
12 N
? m
4.00 m
10 N
18 N
34
Learning Objectives

• To know Newtons Law of Gravitation.
• To understand how gravitational forces keep the
  planets in orbit.
• To understand why planets further from the Sun
  take longer to make one orbit.

35
Gravitational Attraction

• Gravity is a force of attraction between objects.
  It is the force that keeps the planets in orbit,
  but what affects the size of the force of gravity
  between two objects?

36
Gravitational Attraction

• Gravity is an attractive force between two
  objects. The greater the mass of the objects the
  greater the gravitational attraction between
  them. The smaller the distance between the
  objects the greater the gravitational attraction.

F G         
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Gravitational Attraction

• On a space journey the gravitational attraction
  on the rocket decreases as it moves further away
  from the Earth.

38
Gravitational Attraction

• Remember
• Weight (N) Mass (kg) x Gravitational Field
  Strength (N/kg)
• The gravitational field strength on the Earth is
  9.8 N/kg, on the moon it is 1.6 N/kg.
• How much less would a person weighing 94 kg weigh
  on the moon?

39
Keeping the Planets in Orbit

• The centripetal force keeping planets and
  satellites in orbit is gravity. However, they
  must travel at the correct velocity to remain in
  orbit.
• What would happen if we increased the velocity?

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Keeping the Planets in Orbit
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Keeping the Planets in Orbit

• http//www.astro.umass.edu/courseware/java/planets
  /planets.html
• What do you notice about the planets further from
  the Sun?
• What do you know about the force of gravity as
  you get further away?
• How does this relate to the size of centripetal
  force as the radius of the circle increases?

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Keeping the Planets in Orbit

• Planets must move at exactly the right speed to
  stay in orbit. As the force of gravity reduces
  as objects get further from the Sun planets
  further from the Sun orbit more slowly.

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http//hubblesite.org/gallery/album/entire_collect
ion/
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Planetary Orbits Activities

• AQA Physics Page 224 225 Read the pages
  carefully.
• Copy the key points and figure 2.
• Answer summary questions 1 and 2.
• AQA Physics Page 226 227 Read the pages
  carefully.
• Copy the key points.
• Answer summary questions 1 and 2.