Forces

• A force is an interaction (e.g. push, pull or twist) between two objects
• Forces are either contact or non-contact
• Contact forces act by direct contact (touching) on the object  
• Non-contact forces are forces that act at a distance  
• Gravity and magnetism are examples of non-contact forces  
• Drag forces (air and water resistance), friction, tension and normal contact force are examples of contact forces
• Friction is a force between two surfaces that opposes movement
• Tension is a force exerted through a rope, string or wire when pulled by forces at opposite sides
• Forces have size and direction
• Forces are represented on free-body force diagrams using arrows to show the direction and size of the force
• Forces are measured in Newtons (N) using a Newton meter  

Resultant Force

• An objects motion does not change if forces are balanced
• If balanced forces act on a stationary (still) object, it will remain stationary
• If balanced forces act on an object in motion, it will continue moving at the same speed and in the same direction as it was already moving
• Balanced forces are equal in size but opposite in direction
• An unbalanced force can change an objects shape, speed or direction
• The resultant force on an object is the net force or the overall effect of all the forces acting on an object
• When forces are balanced there is a 0 N resultant force
• When forces are unbalanced the resultant force is not 0 N (a non-zero resultant force)
• If forces are acting in the same direction they should be added together to calculate the resultant force
• If forces are acting in opposite directions they should be subtracted
• Resultant force must have a direction
• If there is a resultant force acting on an object, the object will accelerate in the direction of the resultant force
• Forces act in interaction pairs, which can also be called action-reaction pairs
• If object A exerts a force on object B, then object B exerts an equal and opposite force on object A
• The normal contact force is the reaction force exerted by a surface on an object that is resting on it

Effects of Forces

• Changing the shape of an object can be called deformation
• The extension of spring can be measured when different masses are added  
• As more force is added to a spring, the greater the extension (the greater the shape change)
• The extension of a spring is the difference between its stretched length and its original length
• If too much force is added then a spring does not return to its original shape because it has reached its elastic limit
• Force opposing motion is caused by the interaction of surfaces moving over one another
• It is called ‘drag’ if an object is interacting with a fluid, specifically 'air resistance' in air and 'water resistance' in water
• Friction occurs between solids
• Friction and drag forces are contact forces
• The force needed to move a block along different surfaces is measured using a Newtonmeter to investigate friction
• Rougher surfaces generate more friction and smoother surfaces generate less friction
• Friction is reduced by adding lubricant

Disciplinary Knowledge

• Define the terms precise, accurate and valid, and be able to use these terms in the context of data.
• Use SI units (e.g., kg, g, mg; km, m, mm; kJ, J) and IUPAC chemical nomenclature unless inappropriate
• Understand and use the symbols: =, <>, >, ∝, ~
• Identify in a given context:
• the independent variable as the one that is changed or selected by the investigator
• the dependent variable that is measured for each change in the independent variable
• Identify suitable control variables and be able to explain why they are kept the same.
• Decide on a suitable scale for x and y-axis when drawing a graph

Practical Skills

• Read a scale accurately
• Measure and observe the effects of forces including the extension of springs

Gravitational force 

• Gravitational forces act on and between all objects 
• Gravity is an attractive non-contact force between all objects with mass 
• An object which is free to move accelerates towards the centre of the Earth 
• The gravitational field strength of an object is the force exerted per unit of mass at a point in a field 
• The gravitational field strength of an object is increased by its mass 
• The gravitational field strength is decreased by distance from an object
• Non-contact forces are forces that act at a distance 
• Non-contact forces have a force field that weakens with distance 

Mass and Weight  

• Mass is the amount of matter contained in an object and is measured in kg  
• Weight is the force of gravity acting on a mass is measured in Newtons  
• Weight is calculated using the following equation: Weight (N) = mass (kg) x gravitational field strength (N/kg, on Earth g=10 N/kg) 
• Weight is a force so must have a direction (towards the centre of the Earth) 
• When the gravitational field strength changes, the weight of an object will change but the mass will not change 

The Solar System 

• Our solar system contains the Sun, planets orbiting the sun, satellites orbiting planets, asteroid belt and comets 
• Gravity is the force that holds objects in orbit 
• Gravity still acts in space 
• Astronauts on the ISS appear to be floating because they are weightless 
• The planets orbit the Sun; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune 
• Most models of the solar system cannot show the relative distances or sizes of objects 
• Our solar system is a tiny part of one galaxy, one of many billions of galaxies in the universe 
• A light year is the distance light travels in a year (over 9 million, million km) 
• It takes the Earth 365 days to orbit the sun once 
• A satellite is an object that orbits a planet 
• The Moon is the Earth’s natural satellite
• Artificial satellites that orbit the Earth are used for sending waves for communications, navigation and telescopes   
• Planets rotate on their axis which produces day and night; the Earth rotates once every 24 hours but each planet has a different length of day
• The Earth rotates on its tilted axis (of 23.5◦); this produces seasons 
• The Sun is approximately 400 times the size of the Moon but 400 times further away which is how they are able to appear the same size
• In a lunar eclipse the Earth comes between the sun and the moon. The Earth blocks the sunlight from reaching the moon 

Disciplinary Knowledge 

• Use an appropriate number of significant figures 
• Find the arithmetic mean and range of a set of data 
• Substitute numerical values into algebraic equations using appropriate units for physical quantities  
• Solve simple algebraic equations 

Practical Skills 

• Measure and observe the effects of forces including the extension of springs 
• Construct and interpret frequency tables and results tables 
• Consider the best way to present data 
• Decide on a suitable scale for x and y-axis when drawing a graph 
• Construct and interpret bar charts, pie charts and histograms 

Energy Stores 

• Energy cannot be created or destroyed, only transferred between different energy stores 
• Energy is measured in joules (J) 
• 1 joule is a very small amount of energy so often kJ are used 
• Energy can be stored in one or more of: chemical energy store, kinetic energy store, gravitational potential energy store, elastic potential energy store, thermal energy store  
• Food, fuels, cells and batteries are a chemical energy store 
• Food labels show how much energy is stored in the food and are shown in kJ and calories 

 Energy Transfers 

• Energy can be transferred by heating, mechanically, by radiation or by electricity 
• When energy is transferred, the total is conserved, but some energy is dissipated, reducing useful energy
• Energy transfers can be useful or wasteful 
• Wasted energy from appliances, such as heat and sound, dissipates into the surroundings 
• Efficiency is a ratio of how much useful energy has been transferred compared to the total energy transferred 
• Efficiency can be stated as a decimal or percentage
• The higher percentage efficiency, the more useful energy has been transferred 
• Energy transfers are very unlikely to be 100% efficient  
• Sankey diagrams are used to show the efficiencies of energy transfers, where the width of the arrow represents the amount of energy 

Thermal Energy and Transfers 

• Thermal energy moves from hot objects to cold objects until the same temperature (equilibrium) is reached 
• The rate of thermal transfer is greatest when there is a large temperature difference 
• The thermal energy of an object is the total energy of all the particles within it 
• The temperature of an object is the average energy of the particles within it 
• An objects temperature changes over time when heated or cooled. The amount the temperature change depends on the objects mass and what it’s made of 
• When heated, particles move faster in gases and liquids and vibrate more in a solid 
• A conductor allows thermal energy to be transferred through it easily 
• An insulator does not allow thermal energy to be transferred through it easily 

Disciplinary Knowledge 

• Define the terms precise, accurate and valid, and be able to use these terms in the context of data 
• Use an appropriate number of significant figures
• Substitute numerical values into algebraic equations using appropriate units for physical quantities 
• Solve simple algebraic equations 
• Use SI units (e.g., kg, g, mg; km, m, mm; kJ, J) and IUPAC chemical nomenclature unless inappropriate 
• Identify suitable control variables and be able to explain why they are kept the same 
• Interconvert units 

Practical Skills  

• Measure temperature accurately 
• Construct and interpret bar charts, pie charts and histograms 
• Plot two variables from experimental or other data 
• Safe use of appropriate apparatus to measure energy changes/ transfers and associated values such as work done 

Electric Circuits 

• Models can be used to describe how a circuit works but no model is perfect because they are not the same as the live phenomenon
• In a series circuit there is only one path for the current to take 
• In a parallel circuit there are multiple paths (or branches) 
• If a component in a series circuit breaks, the circuit is now incomplete 
• If a component in a parallel circuit breaks there may still be another path for the current to flow, depending on the location of the circuit break 
• The following are common circuit components: cell, battery, bulb/lamp, motor, switch, buzzer, ammeter, voltmeter 
• A battery is a group of cells working together 

Current 

• Current is the rate of flow of charge 
• Current is measured in Amperes/Amps (A) using an Ammeter 
• Ammeters are placed in series 
• Current transfers energy 
• Current can be calculated with the following equation:

Current (A) = Charge (C)

                        Time (s)

• Charge is measured in Coulombs (C) 
• For current to flow there needs to be a complete circuit and a power supply or battery to push the charges around the circuit 
• Current is the same everywhere in a series circuit
• Current splits at the junctions in a parallel circuit 

Voltage 

• Voltage is measured in Volts (V) using a Voltmeter 
• Voltmeters are placed in parallel 
• Voltage is the amount of energy shifted from the power source to the moving charge, or from the charge to the circuit component in V 
• Adding voltage increases the current and increases the brightness of bulbs 
• Brightness of a bulb is decreased with more bulbs (components) added  
• A battery with a higher voltage is able to give the charges a larger push around the circuit 
• A battery that is bigger in size is able to store more charge so lasts longer 
• Voltage is shared between components in series circuits 
• Voltage is the same in branches of a parallel circuit 

Disciplinary Knowledge 

• Use models to represent data, events, processes, behaviours and other scientific phenomena 

Select the best procedure from given options 

• Explain why a given practical procedure is well designed for its specified purpose.  
• Apply understanding of apparatus and techniques to suggest a procedure for a specified purpose.

• Use of circuit diagrams to construct and check series and parallel circuits including a variety of common circuit elements 

Practical Skills  

Use of appropriate apparatus to measure current, potential difference (voltage) and resistance, and to explore the characteristics of a variety of circuit elements