IGCSE Physics Key Definitions  Motion Forces and Energy For 0625 AND 0972  (9-1)

Motion , Forces and Energy

Topic 1: Motion, forces, and energy

1.1 Physical quantities and measurement techniques

• Define scalar quantity: A scalar quantity is a quantity that has magnitude (size) only. Examples of scalars: distance, speed, time, mass, energy and temperature
• Define vector quantity: A vector quantity is a quantity has magnitude and direction. Examples of vectors: force, weight, velocity, acceleration, momentum, electric field strength and gravitational field strength

1.2 Motion

• Define speed: Speed is the distance travelled per unit time
• Define acceleration: Acceleration is the change in velocity per unit time
• Define velocity: Velocity is the speed in a given direction
• Define Average speed: Average speed is defined as total distance / Total time
• Define Free-fall: An object is in free-fall   when it is moving only under the influence of the earth’s gravity. 
• Define Acceleration of free fall: It is a value of the acceleration of free fall (g). On Earth, this value of g for any object that is near the surface is approximately constant at  9.8m/s². [ In IGCSE examinations, this value is taken to be 10m/s²]

1.3 Mass and weight:

• Define Mass: Mass is a measure of the quantity of matter in an object at rest relative to the observer
• Define Weight: Weight is defined as a gravitational force on an object that has mass
• Define Gravitational field strength: Gravitational field strength is  the  force per unit mass

1.4 Density

• Define density: Density is defined as the  mass per unit volume

1.5 Forces

• Define Spring constant: Spring constant is defined  as the  force per unit extension. Its formula is: k=F/x
• Define Limit of proportionality: It is a point beyond which the spring crosses its elastic limit and becomes permanently deformed.
• State Newtons second law: It states that, for a body of constant mass "m" and net force "F", we can state that F = ma, where F ( net force) and a (acceleration)/ Both  are vector quantities. 
• Define Circular motion: Circular motion is defined as the movement of an object along the circumference of a circle or the rotation of an object along a circular path. 
• Define Solid friction: Solid friction as the force between two surfaces that may impede motion and produce heating.
• Define Drag force: It is a force acting in a direction that is opposite to the relative motion of the object moving with respect to the surrounding fluid. Fluid refers to liquids and gases 
• Define Moment of a force: It is a measure of the turning effect of a force. Formula is moment = force × perpendicular distance from the pivot. The SI unit of moment of a force is Nm
• State the Principle of moments: For an object in equilibrium, the sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments about the same point and the net force acting on it is zero.
• Define Centre of gravity: It is a point at which the weight of a body or system is supposed to be concentrated. In uniform gravity it is the same as the centre of mass.
• Define Momentum: Momentum=mass × velocity; recall and use the equation p = mv. The SI unit of momentum is kgm/s
• Define Impulse: Impulse= force × change in time. [ it is the time for which force acts]. The Si unit of impulse is Newton-second (Ns)
• State the Principle of conservation of momentum: When 2 or more bodies interact (collide) in an isolated system, the total momentum stays the same.
• Define Resultant force: A resultant force is the change in momentum per unit time. The unit is Newtons (N)
• Define Kinetic energy: The energy possessed by an object, by virtue of its motion is called as kinetic energy.
• Define Gravitational potential energy: When objects are placed in a gravitational field, they possess certain energy relative to their position in this gravitational field. This energy is called as the gravitational potential energy. Formula for the gravitational potential energy= mgh; here m=mass of the object, g=gravitational field strength and h is the height to which the object is raised.
• Define Chemical energy: The energy stored in the bonds of chemical compounds is called as the chemical energy.
• Define Elastic (Strain energy): Strain energy is the energy stored in an object due to its deformation.
• Define Electrostatic energy: It refers to the potential energy of a system of separated electric charges
• Define Internal (Thermal) energy:The energy of a thermodynamic system is its internal energy.  It is the energy associated with the random, disordered motion of molecules
• State the Principle of conservation of energy: Principle of conservation of energy states that " Energy can never be created nor destroyed. It can only be converted from one form to another. The total amount of energy in a system stays the same.
• Define Work: Work is= Force x displacement. Here the displacement is in the direction of the force. Unit of work is Joule.
• Define One Joule: One Joule refers to the work done by a force of 1 Newton, when it displaces a body through 1m in the direction of the force applied.
• Define Solar cells [ Photovoltaic cells]: This refers to cells that are capable of converting light energy to electrical energy through photovoltaic effect
• Define Solar panels: [ Photo-voltaic panel/Solar-electric panel]: It is a panel consisting of many solar cells, designed to absorb sun’s rays for generating electricity or for heating purposes.
• Define Wind energy: The energy of the naturally flowing air that is used to generate electricity is called as wind energy.
• Define Renewable energy resources: This is the type of energy that comes from resources that are easily replenished. Example: Energy from the sun, wind, etc.
• Define Non-renewable energy: This is the type of energy that comes from resources that are easily not easily replenished. Example: Energy from fossil fuels
• Define  Percentage Efficiency: Percentage efficiency= {[ Useful energy output] /Total energy input]} x 100  or   { [ Useful power output] /Total power  input]} x 100 
• Define Power: Power is defined as the work done per unit time  of power is defined as the  energy transferred per unit time.SI unit  power is Watts (W)
• Define Pressure: Pressure is defined as the force per unit area.SI unit of pressure if Pascals (Pa). Formula for calculating pressure due to solids=Force/Area; While the formula to calculate the pressure exerted due to liquids is=hpg. Where h is the height of the liquid column, p is the density of the liquid and g is the gravitational field strength.

Topic 2:  IGCSE Physics Thermal Physics Definitions

Topic 3: IGCSE Physics Waves  Definitions

 Topic 4: IGCSE Physics Electricity and Magnetism Definitions

  Topic 4: IGCSE Physics  Space  Physics  Definitions