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Revision Planner Page
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Forces Forces and elasticity Moments, levers and gears Pressure in a fluid Speed and velocity Distance–time and velocity–time graphs
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Newton’s laws Forces and braking Momentum Energy transfers Conservation and dissipation of energy National and global energy resources
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36
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Transverse and longitudinal waves Sound waves and reflection of waves Waves for detection and exploration Electromagnetic waves and properties 1 Electromagnetic waves and properties 2
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46
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Lenses and visible light Black body radiation Circuits, charge and current Current, resistance and potential difference Series and parallel circuits
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DAY 5 DAY 6 DAY 7
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56
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Domestic uses and safety Energy transfers Static electricity Permanent and induced magnetism, magnetic forces and fields Fleming’s left-hand rule, electric motors and loudspeakers
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HT 58
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62 64 66
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Induced potential and transformers Changes of state and the particle model Particle model and pressure Atoms and isotopes Radioactive decay, nuclear radiation and nuclear equations
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68
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72 74
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Half-lives and the random nature of radioactive decay Hazards and uses of radioactive emissions and background radiation Nuclear fission and fusion Our solar system and the life cycle of a star Orbital motion, natural and artificial satellites
78 90 92 93 95 96
Answers Glossary The Periodic Table Physics equations Index Acknowledgements
HT WS
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indicates content that is Higher Tier only. indicates ‘Working Scientifically’ content, which covers practical skills and data-related concepts. 3
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18/12/2017 10:56
DAY 1
30 Minutes
Forces Scalar quantities have magnitude only. Vector quantities have magnitude and an associated direction. A vector quantity can be represented by an arrow. The length of the arrow represents the magnitude, and the direction of the arrow represents the direction of the vector quantity.
Contact and non-contact forces A force is a push or pull that acts on an object due to the interaction with another object. Force is a vector quantity. All forces between objects are either: contact forces – the objects are physically touching, for example: friction, air resistance, tension and normal contact force or non-contact forces – the objects are physically separated, for example: gravitational force, electrostatic force and magnetic force.
Air resistance
Gravity Weight is the force acting on an object due to gravity. All matter has a gravitational field that causes attraction. The field strength is much greater for massive objects. The force of gravity close to the Earth is due to the gravitational field around the Earth. The weight of an object depends on the gravitational field strength at the point where the object is. The weight of an object and the mass of an object are directly proportional (weight ⬀ mass). Weight is a vector quantity as it has a magnitude and a direction. Mass is a scalar quantity as it only has a magnitude. Weight is measured using a calibrated spring-balance – a newtonmeter. Weight can be calculated using the following equation: weight = mass × gravitational field strength W = mg weight, W, in newtons, N mass, m, in kilograms, kg gravitational field strength, g, in newtons per kilogram, N/kg
Friction
Example What is the weight of an object with a mass of 54 kg in a gravitational field strength of 10 N/kg? weight = mass × gravitational field strength = 54 kg × 10 N/kg = 540 Nm
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Resultant forces The resultant force equals the total effect of all the different forces acting on an object. HT 20 kN When the truck is accelerating, the forces on it are unbalanced 10 kN
1 kN
If the forces on an object are balanced, the resultant force is zero. If the object is stationary it remains stationary and if it is moving it continues moving at a constant speed.
SUMMARY Force is a vector quantity. A force is a push or pull that acts on an object due to the interaction with another object. Resultant force equals the total effect of all the different forces acting on an object. Work is done when a force causes an object to move.
QUESTIONS The resultant force is therefore 9 kN 20 kN 9 kN
A single force can be resolved into two components acting at right angles to each other. The two component forces together have the same effect as the single force.
Work done and energy transfer Work is done when a force causes an object to move. The force causes a displacement. The work done by a force on an object can be calculated using the following equation: work done = force × W = Fs
distance moved along the line of action of the force
work done, W, in joules, J force, F, in newtons, N distance, s, in metres, m (s represents displacement, commonly called distance)
Example What work is done when a force of 90 N moves an object 14 m? work done = force × distance moved along the line of action of the force
QUICK TEST 1. What is a vector quantity? 2. What is a scalar quantity? 3. What is the weight of a 33 g object in a gravitational field strength of 10 N/kg? 4. What is 57 Nm in joules?
EXAM PRACTICE 1. In a warehouse a metal crate is pushed 4 m along the floor by a force of 320 N. a) The weight of the crate is 560 N. Assuming a gravitational field strength of 9.8 N/kg, what is the mass of the crate? b) What work is done pushing this crate?
[2 marks] [2 marks]
c) Pushing the crate is an example of exerting a contact force; if the crate was pulled by a magnet this would be an example of a non-contact force. Explain this difference.
[2 marks]
work done = 90 × 14 = 1260 J One joule of work is done when a force of one newton causes a displacement of one metre. 1 joule = 1 newton metre Work done against the frictional forces acting on an object causes a rise in the temperature of the object. 5
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21/04/2023 13:59
DAY 1
25 Minutes
Forces and elasticity Spring balance
Plastic Deformation When an object is stretched and returns to its original length after the force is removed, it is elastically deformed. When an object does not return to its original length after the force has been removed, it is inelastically deformed. This is plastic deformation.
Extension The extension of an elastic object, such as a spring, is directly proportional to the force applied (extension ⬀ force applied), if the limit of proportionality is not exceeded. Stretching – when a spring is stretched, the force pulling it exceeds the force of the spring. Bending – when a shelf bends under the weight of too many books, the downward force is from the weight of the books, and the shelf is resisting this weight. Compressing – when a car goes over a bump in the road, the force upwards is opposed by the springs in the car’s suspension.
In order for any of these processes to occur, there must be more than one force applied to the object to bring about the change. The force on a spring can be calculated using the following equation: force = spring constant × extension F = ke force, F, in newtons, N spring constant, k, in newtons per metre, N/m extension, e, in metres, m
Example A spring with spring constant 35 N/m is extended by 0.3 m. What is the force on the spring? F = ke = 35 × 0.3 = 10.5 N This relationship also applies to the compression of an elastic object, where the extension, e, would be the compression of the object. A force that stretches (or compresses) a spring does work and elastic potential energy is stored in the spring. Provided the spring does not go past the limit of proportionality, the work done on the spring equals the stored elastic potential energy.
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Force and extension
SUMMARY
Force and extension have a linear relationship. If force and extension are plotted on a graph, the points can be connected with a straight line (see Graph 1). The points in a non-linear relationship cannot be connected by a straight line (see Graph 2).
An object that doesn’t return to its original length when the stretching force is removed is called inelastically deformed.
Graph 1 – Linear relationship 50
Force and extension have a linear relationship if the limit of proportionality has not been reached.
Force, F (N)
40 30
An object that returns to its original length when the stretching force is removed is called elastically deformed.
Slope of graph gives the spring constant, k
20
QUESTIONS
10 0 0.00
0.02
0.04
0.06 0.08 0.10 Extension, e (m)
0.12
0.14
1. What is meant by elastically deformed? 2. What is the force of a spring with an extension of 0.3 m and a spring constant of 2 N/m?
Graph 2 – Non-linear relationship
3. What energy store is increased when a spring is stretched?
14
Force, F (N)
12 10
EXAM PRACTICE
8
1. An investigation was carried out into the deformation of an elastic thread.
6 4 2 0 0.00
QUICK TEST
0.02
0.04
0.06 0.08 0.10 Extension, e (m)
0.12
0.14
In order to calculate the spring constant in Graph 1, take two points on the line and apply the equation. Two points: (0, 0) and (0.12, 30) change in force
So, spring constant = change in extension 30 – 0 = 0.12 –0
= 250 N/m
a) The elastic thread was stretched by a force of 7 N. The spring constant of the elastic thread was 18 N/m. How far was the elastic thread extended?
[2 marks]
b) The elastic thread was stretched again with a number of different forces. Force and extension were then plotted on a graph. The thread did not exceed the limit of proportionality. i) Predict what type of line could be used to connect the points on the graph. [1 mark] ii) What type of relationship is shown by these results?
[1 mark]
iii) If the thread had exceeded the limits of proportionality, would the results show a different relationship? Explain your answer.
[2 marks]
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16/06/2023 10:21
DAY 1
30 Minutes
Moments, levers and gears Moments The turning effect of a force is called the moment of the force. The moment of a force is given by the following equation: moment of a force = force × distance to pivot M = Fd moment of a force, M, in newton metres, Nm force, F, in newtons, N distance to pivot, d, is the perpendicular distance from the pivot to the line of action of the force, in metres, m
Example A 30 cm spanner is used with a force of 36 N. What is the moment? M = Fd = 36 × 0.3 = 10.8 Nm If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot. the sum of the sum of = clockwise moments anticlockwise moments For example:
1.5 m 3m
10 N
20 N
Moment = 10 × 3 = 30 Nm
Moment = 20 × 1.5 = 30 Nm Pivot
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SUMMARY The moment is the turning effect of a force. Using a lever reduces the force needed to carry out an action. Both levers and gears act as force multipliers. This means they exert a larger force than is being exerted on them.
QUESTIONS Levers and gears A lever reduces the force needed to carry out an action. The force is exerted around a pivot. Levers and gears systems can both be used to transmit the rotational effects of forces. Levers and gears act as force multipliers, exerting a larger force than is being exerted on them. For example: A force of 400 N would lift the weight as moment = 400 × 2 = 800 Nm
Moment = 800 N × 1 = 800 Nm
800 N
2m
QUICK TEST 1. If gears in a system are different sizes, the smaller gear will rotate faster than the larger gear. True or false? 2. What is a moment? 3. What is the moment when a force of 50 N is applied with a 0.4 m lever?
EXAM PRACTICE 1. A child sitting on a seesaw exerts a force of 400 N and has a moment of 600 Nm. a) How far is the child sitting from the pivot?
1m
A gear system can also be used to transfer the rotational effect of forces. The teeth of gears interlock so when the first gear in a system rotates, it rotates the other gears that it is interlocked with. Two interconnected gears will rotate in opposite directions. Output Input
[2 marks]
b) How far would a child who exerts a force of 300 N have to sit from the pivot to balance the seesaw? Show how you arrived at your answer.
[2 marks]
2. A gear rotates at a speed of 60 rotations a second. It interlocked with a larger gear. What statement could be made about the rotational speed of the larger gear? Explain your answer.
[2 marks]
If gears are different sizes, the smaller gear in a system will rotate faster than the larger gear. 9
76065_P004_P015_RP2.indd 9
22/02/2023 16:07
DAY 1
25 Minutes
Pressure in a fluid Fluids Liquids and gases are fluids. The pressure in a fluid is caused by the fluid and the surrounding atmospheric pressure. The pressure causes a force to act at right angles (normal) to a surface. The pressure exerted on a surface by a fluid can be calculated using the following equation: normal to a surface pressure = force area of that surface F p=A
pressure, p, in pascals, Pa force, F, in newtons, N area, A, in metres squared, m2
Example What is the pressure of a force of 650 N over an area of 0.50 m2? normal to a surface pressure = force area of that surface
= 650 0.5
= 1300 Pa Liquids are relatively incompressible and the pressure in liquid is transmitted equally in all directions, meaning hydraulic systems containing liquids can be used to transmit pressure and so magnify a force.
HT
The pressure exerted by a column of liquid can be calculated using the following equation:
height density gravitational field pressure = of the × of the × liquid column strength p = h g pressure, p, in pascals, Pa height of the column, h, in metres, m density, , in kilograms per metre cubed, kg/m3 gravitational field strength, g, in newtons per kilogram, N/kg
Example What is the pressure at a depth of 40 m in seawater? (density of seawater = 1029 kg/m3 and gravitational field strength = 10 N/kg) pressure = 40 × 1029 × 10 = 411.6 kPa When the height of a column of liquid increases or the density of the liquid increases, there are more particles above the base of the column, so their total weight is greater. This greater force on the base of the column increases the pressure.
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HT
SUMMARY
Upthrust
A submerged object experiences a greater pressure on the bottom surface than on the top surface. This creates an upward force called upthrust.
The pressure in a fluid is caused by the fluid and the surrounding atmospheric pressure.
An object less dense than the surrounding liquid displaces a volume of liquid equal to its own weight. This object floats as its weight is equal to the upthrust.
Liquids and gases are fluids.
An object more dense than the surrounding liquid is unable to displace a volume of liquid equal to its own weight. This object sinks as its weight is greater than the upthrust.
The thin layer of air around the Earth is called the atmosphere.
HT Upthrust is the upward force that results when
a submerged object experiences greater pressure on the bottom surface than the top.
As the height of an object increases, the atmospheric pressure decreases.
The boat floats as weight and upthrust are equal
QUESTIONS QUICK TEST 1. Explain why air pressure decreases with height.
The anchor sinks as its weight is greater than the upthrust
HT 2.
What is the pressure in a 19 m column of water? (density of water = 1000 kg/m3 and gravitational field strength = 10 N/kg)
HT 3.
What is upthrust?
EXAM PRACTICE Atmospheric pressure The atmosphere is a thin layer (relative to the size of the Earth) of air round the Earth. The atmosphere gets less dense with increasing altitude. The air molecules colliding with a surface create atmospheric pressure. As height of an object increases, there are fewer air molecules above the object so their total weight is smaller. This leads to a lower atmospheric pressure.
1. A hydraulic system uses liquids to transmit pressure and magnify a force. a) Explain why liquids are used in hydraulic systems instead of gases. [2 marks] b) In a hydraulic system, what force is exerted when the pressure is 1200 Pa and [2 marks] the area of the surface is 0.2m2 ? HT 2.
A student carried out an investigation into floating and sinking of model boats using different materials. a) Her first boat sank. Explain, in terms of forces, why this occurred.
[2 marks]
b) How could the student modify her boat to increase the chance of it floating? [2 marks]
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