AQA GCSE Physics 31 Turning Forces

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AQA GCSE Physics 3-1Turning Forces

• GCSE Physics pages 214 to 233

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AQA GCSE Specification

• MOMENTS STABILITY
• 13.1 How do forces have a turning effect?
• Using skills, knowledge and understanding of how
  science works
• to describe how to find the centre of mass of
  a thin sheet of a material
• to calculate the size of a force, or its
  distance from an axis of rotation, acting on a
  body that is balanced
• to analyse the stability of bodies by
  considering their tendency to topple.
• Skills, knowledge and understanding of how
  science works set in the context of
• The turning effect of a force is called the
  moment.
• The size of the moment is given by the
  equation
• moment force perpendicular distance from the
• line of action of the force to the axis of
  rotation
• The centre of mass of a body is that point at
  which the mass of the body may be thought to be
  concentrated.
• If suspended, a body will come to rest with
  its centre of mass directly below the point of
  suspension.
• The centre of mass of a symmetrical body is
  along the axis of symmetry.
• If a body is not turning, the total clockwise
  moment must be exactly balanced by the total
  anticlockwise moment about any axis.
• Recognise the factors that affect the
  stability of a body.
• If the line of action of the weight of a body
  lies outside the base of the body there will be a
  resultant moment and the body will tend to
  topple.

• Skills, knowledge and understanding of how
  science works set in the context of
• When a body moves in a circle it continuously
  accelerates towards the centre of the circle.
  This acceleration changes the direction of motion
  of the body, not its speed.
• The resultant force causing this acceleration
  is called the centripetal force.
• The direction of the centripetal force is
  always towards the centre of the circle.
• The centripetal force needed to make a body
  perform circular motion increases as
• the mass of the body increases
• the speed of the body increases
• the radius of the circle decreases.
• SATELLITE AND PLANETARY MOTION
• 13.3 What provides the centripetal force for
• planets and satellites?
• Using skills, knowledge and understanding of how
  science works
• to interpret data on planets and satellites
  moving in orbits that approximate to circular
  paths.
• Skills, knowledge and understanding of how
  science works set in the context of
• The Earth, Sun, Moon and all other bodies
  attract each other with a force called gravity.

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MomentsNotes questions from pages 214 215

• What is meant by the moment of a force?
• Copy Figure 2 on page 214 and explain how a lever
  can used to lift a heavy load.
• Copy and answer questions (a) and (b) on page
  214.
• Copy the equation at the top of page 215 along
  with the units used.
• Copy and answer questions (c) and (d) on page
  215.
• Copy the Key points table on page 215.
• Answer the summary questions on page 215.

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Moments ANSWERS

• In text questions
• Either the spanner bends or it deforms the nut.
• A long one.
• The moment increases.
• 21 Nm

• Summary questions
• (a) Anticlockwise
• (b) (i) Increased
• (ii) Decreased
• (a) (i) The moment of the force you apply is
  greater so more force is applied to the nail to
  remove it.
• (ii) The moment needed to turn a rusty hinge is
  greater so more force is needed compared with an
  oiled hinge.
• (b) 72 N

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Centre of mass Notes questions from pages 216
217

• What is meant by the centre of mass of an
  object?
• Copy and answer question (a) on page 216.
• Draw both diagrams of Figure 3 on page 217.
• Describe an experiment to find the centre of mass
  of an irregular shaped object. You should include
  a diagram like that of Figure 4 on page 217 as
  part of your answer.
• Copy the Key points table on page 217.
• Answer the summary questions on page 217.

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Centre of mass ANSWERS

• In text questions
• If the ruler is uniform, the centre of mass is at
  the centre.

• Summary questions
• (a) and (c) At the point where the diagonals
  meet.
• (b) At its centre.
• 2. The weight of the child has a turning effect
  about the top of the swing when the childs
  centre of mass is not directly below the top. The
  turning effect makes the child return to the
  centre.

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Moments in balance Notes questions from pages
218 219

• Copy Figures 1 and 2 on page 218 and then copy
  and answer question (a) on page 218.
• What is the Principle of Moments?
• Copy and answer questions (b), (c) and (d) on
  pages 218 and 219.
• Explain how a wheelbarrow allows the
  transportation of heavy objects. Copy the top
  diagram of Figure 4 on page 219 as part of your
  answer.
• Copy the Key points table on page 219.
• Answer the summary questions on page 219.

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Moments in balance ANSWERS

• In text questions
• Her moment about the pivot must equal the moment
  of the boy about the pivot. The moment is her
  weight x the distance from the pivot. Because she
  is heavier, she needs to be nearer the pivot than
  the boy to give an equal moment to the boys
  moment.
• 2.5 N
• 1.2 N
• The effort acts further from the pivot than the
  load does. So a smaller effort gives an equal and
  opposite moment to a larger load.

• Summary questions
• (a) Jasmin.
• (b) 340 N
• (c) 1.89 m
• 2. (a) 1.5 N
• (b) 1.5 N

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Stability Notes questions from pages 220 221

• Copy Figure 1 on page 220 and explain the process
  by which the brick becomes unstable as it is
  tilted.
• Copy and answer questions (a) and (b) on page
  220.
• Copy Figure 2 on page 220 and explain why the
  wheelbase of a tractor should be as wide as
  possible.
• Copy and answer questions (c), (d) and (e) on
  pages 220 and 221.
• Copy the Key points table on page 221.
• Answer the summary questions on page 221.

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Stability ANSWERS

• In text questions
• Its weight acts through the point of contact so
  it has no turning effect.
• People open an upper drawer that produces a
  turning force that topples the filing cabinet.
• So its centre of mass is as low as possible,
  which makes it more stable.
• Less stable.
• To provide a wider base if the child loses
  balance.

• Summary questions
• 1. (a) A table, a low-loader vehicle, a traffic
  cone, etc.
• (b) A supermarket trolley, a tall electric
  kettle, etc.
• (a) A chair would topple over if the baby in the
  chair leans too far sideways.
• (b) The lower the centre of mass, the harder it
  is to topple it over.

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Circular motionNotes questions from pages 222
223

• Explain why an object moving in a circle has a
  centrally directed acceleration by copying the
  bullet points below Figure 2 on page 222.
• Copy and answer question (a) on page 222.
• What is a centripetal force? Give two examples
  of centripetal force.
• Copy and answer question (b) on page 223.
• What factors affect the size of the centripetal
  force acting on an object moving in a circle?
• Copy and answer question (c) on page 223.
• Copy the Key points table on page 223.
• Answer the summary questions on page 223.

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Circular motion ANSWERS

• In text questions
• It would fly off at a tangent.
• The force of gravity due to the Earth on it.
• There is much less friction so the centripetal
  force is less and the car must go slower.

• Summary questions
• (a) D, C.
• (b) C, B.
• 2. (a) Friction.
• (b) Pull (tension).
• (c) Gravity.
• (d) Electrostatic force.

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Gravitational attraction Notes questions from
pages 224 225

• State Newtons rules on gravity.
• Copy and answer questions (a) and (b) on page
  224.
• Describe how the force of gravity on a space
  vehicle changes as it travels from the Earth to
  the Moon.
• Copy and answer question (c) on page 224.
• Define what is meant by gravitational field
  strength. Show that a mass of 200 kg weighs
  approximately 32 N on the Moon.
• Copy and answer question (d) on page 225.
• Copy the Key points table on page 225.
• Answer the summary questions on page 225.

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Gravitational attraction ANSWERS

• In text questions
• The force of gravity on it due to the Sun.
• Their mass is too small.
• The force of gravity on the Moon is less, so less
  energy would be needed to escape from the Moon.
• The force of gravity due to the Earth.

• Summary questions
• (a) Increases
• (b) Stays the same
• (c) Decreases.
• 2. (a) The force of gravity is less on the Moon
  so it is easier for the astronaut to move up and
  down.
• (b) The force of gravity is less on the Moon so
  the ball can go higher for the same change of
  gravitational potential energy.

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Planetary orbits Notes questions from pages 226
227

• Copy the table on page 227.
• (a) What force is responsible for planetary
  motion? (b) Why is this force an example of
  centripetal force?
• Explain how orbital speed affects the shape of a
  planets orbit.
• State how (a) the speed and (b) the time taken to
  complete one orbit depends on a planets distance
  from the Sun.
• Copy and answer questions (a) and (b) on pages
  226 and 227.
• Copy the Key points table on page 227.
• Answer the summary questions on page 227.

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Planetary orbits ANSWERS

• In text questions
• There would probably be a bigger variation of
  temperature each year. The tides would be more
  variable.
• Its orbit is about 5 times bigger and it takes
  about 12 times longer, so it must travel slower
  than the Earth.

• Summary questions
• (a) Satellite, Sun.
• (b) Earth
• (c) Satellite, Earth.
• (d) Planet, Sun.
• 2. (a) (i) Jupiter (ii) Venus
• (b) 49 km/s

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SatellitesNotes questions from pages 228 229

• with the aid of a diagram explain how a satellite
  can remain in orbit about the Earth.
• How does (a) the speed and (b) the period of a
  satellite vary with its height above the Earth?
• Copy and answer questions (a) and (b) on page
  228.
• (a) What is meant by a geostationary orbit? (b)
  Why must satellite TV use geostationary
  satellites?
• What are monitoring satellites? What type of
  orbit is used for this type of satellite?
• Copy and answer question (c) on page 229.
• Copy the Key points table on page 229.
• Answer the summary questions on page 229.

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Satellites ANSWERS

• In text questions
• It can give the location and the height above sea
  level.
• 12
• They would be slowed by drag from the atmosphere
  and would fall back to Earth.

• Summary questions
• (a) High, equator.
• (b) Low, poles.
• 2. (a) (i) Below (ii) Above
• (b) Less energy is needed because the orbit
  is nearer the ground than a geostationary orbit
  is.

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Turning issuesNotes questions from pages 230
231

• No questions.

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How Science Works ANSWERS

• Force, mass or moment.
• The distance the tip of the board moves down.
• Range based on diver masses and/or the position
  from where the diver will take off.
• At least five.
• Probably millimetres
• Depends on chosen independent variable.
• For example with force controls would be
  position on board, width of board etc.
• (g) Table should be clear and contain headings
  for the independent and dependent variables along
  with their units. Space should also be provided
  for repeated measurements and average
  calculations.