IGCSE Physics Motion Forces and Energy key definitions

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

Motion , Forces and Energy

igcse-physics-definition-laws 

OBJECTIVES:

By the end of this section, you will be able to :

  • Define key terms for IGCSE Physics for 0625 and 0972 (9-1) 
  • Understand how marks have been allotted in the examination questions  for defining various quantities
  • Become extremely confident in defining various terms using the correct scientific vocabulary as per the syllabus requirements

IGCSE Physics Definitions — Topic 1: Motion, forces, and energy

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  • Scalar quantity

    A scalar quantity is a quantity that has magnitude (size) only. Examples of scalars: distance, speed, time, mass, energy and temperature

  • 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

  • Speed

    Speed is the distance travelled per unit time

  • Acceleration

    Acceleration is the change in velocity per unit time

  • Velocity

    Velocity is the speed in a given direction

  • Average speed

    Average speed is defined as total distance / Total time

  • Free-fall

    An object is in free-fall when it is moving only under the influence of the earth’s gravity.

  • 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]

  • Mass

    Mass is a measure of the quantity of matter in an object at rest relative to the observer

  • Weight

    Weight is defined as a gravitational force on an object that has mass

  • Gravitational field strength

    Gravitational field strength is the force per unit mass

  • Density

    Density is defined as the mass per unit volume

  • Spring constant

    Spring constant is defined as the force per unit extension. Its formula is: k=F/x

  • Limit of proportionality

    It is a point beyond which the spring crosses its elastic limit and becomes permanently deformed.

  • 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.

  • 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.

  • Solid friction

    Solid friction as the force between two surfaces that may impede motion and produce heating.

  • 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

  • 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

  • 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.

  • 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.

  • Momentum

    Momentum=mass × velocity; recall and use the equation p = mv. The SI unit of momentum is kgm/s

  • Impulse

    Impulse= force × change in time. [ it is the time for which force acts]. The Si unit of impulse is Newton-second (Ns)

  • Principle of conservation of momentum

    When 2 or more bodies interact (collide) in an isolated system, the total momentum stays the same.

  • Resultant force

    A resultant force is the change in momentum per unit time. The unit is Newtons (N)

  • Kinetic energy

    The energy possessed by an object, by virtue of its motion is called as kinetic energy.

  • 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.

  • Chemical energy

    The energy stored in the bonds of chemical compounds is called as the chemical energy.

  • Elastic (Strain energy)

    Strain energy is the energy stored in an object due to its deformation.

  • Electrostatic energy

    It refers to the potential energy of a system of separated electric charges

  • 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

  • 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.

  • Work

    Work is= Force x displacement. Here the displacement is in the direction of the force. Unit of work is Joule.

  • 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.

  • Solar cells [ Photovoltaic cells]

    This refers to cells that are capable of converting light energy to electrical energy through photovoltaic effect

  • 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.

  • Wind energy

    The energy of the naturally flowing air that is used to generate electricity is called as wind energy.

  • Renewable energy resources

    This is the type of energy that comes from resources that are easily replenished. Example: Energy from the sun, wind, etc.

  • Non-renewable energy

    This is the type of energy that comes from resources that are easily not easily replenished. Example: Energy from fossil fuels

  • Percentage Efficiency

    Percentage efficiency= {[ Useful energy output] /Total energy input]} x 100 or { [ Useful power output] /Total power input]} x 100

  • 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)

  • 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.

 

 

 

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