AS physics unit 1

Base unit

Units from which all other units are derived

Derived unit

Two or more bass units

Homogeneous equations (don’t really need to know)

For an equation to be valid is that each of the terms in the equations need to have the same base unit

Vector

A physical quantity that needs a magnitude a unit and direction

EG displacement, velocity, acceleration, force, electric current, momentum

Scalar

A physical quantity that requires only a magnitude and a unit

EG distance, speed, time, KE, time

Equilibrium of forces (kinda) also know as translational equilibrium

Up forces = down forces and left forces = right forces

Moment of a force

‘MOAF’ about a point is defined as the product of the force and the perpendicular distance from the point to the line of action of the force

M= FxD

Centre of gravity

Of an object is the point which we can take it’s WEIGHT to act

Centre of mass

Of an object is the point at which we take its MASS to be concentrated

Principle of moments

States that when an object is in rotational equilibrium the sun of the clockwise moments about any point is equal to the sun of the anti-clockwise moments about the same point

ACM = CM

Displacement

Is the distance moved in a particular direction

Speed

Distance moved per second

Velocity

Displacement per second

Acceleration

The rate of change of velocity with time

Equations of motion ( UVATS) 4 of them

v = u + at

s = ut + ½ at2. (Squared)

V2 = u2 + 2as ( v and u squared)

S = (u+v)/2t

Parabola

The curved path which particles in projectile motion follow

Time of flight

Time for constant horizontal velocity to cover range

OR

Total time the projectile spends in the air

Max height

When vertical velocity reaches zero or height half way through time of flight

Range

Horizontal velocity X time of flight

Newtons First law of motion

If a body is at rest it will remain at rest unless a resultant force acts on the object. If the body is moving in a straight line with a constant speed it will continue to move this way unless a resultant force acts on it.

Newtons Second law of motion

for a body lf constant mass it’s acceleration is directly proportional to the resultant force applied and in the direction of the resultant force

RF= ma

Newtons Third law of motion

Whenever one body exerts a force another, the second body exerts an equal and opposite force on the first body

Unit of force ( the newton)

The force needed to cause a mass of 1kg to have an acceleration of 1m/s2

Momentum of a body

The product of its mass and its velocity

p = mv

Principle of conservation of linear momentum

If no external forces are acting the total momentum of a system of colliding bodies is constant

Newton’s second law of motion and momentum

The change of momentum per second is equal to the applied force and the momentum change take place in the direction of the force

Impulse

The product of force and time

Ft = m(v-u)

m(v-u) aka change in momentum

Application of the conservative of momentum (equation)

(All numbers the smaller ones)

m1u1 + m2u2 = m1v1 + m2v2

Collisions

Momentum is conserved

Loss of KE transferee to different forms eg heat sound or potential

Elastic collisions

Kinetic energy is conserved

Inelastic collisions

Kinetic energy is NOT conserved

Kinetic energy ( equation)

KE = ½ mv2

Energy

Defined as the stored ability to do work

Work done

Define by a constant force as the product of the force and distance moved in in the direction of the force

W = F x s Unit is joules J

s = distance

Gravitational potential energy

Is the energy possessed by an object due to its raised position above the earths surface

GPE = mgh

Kinetic energy

Energy of momentum

K.E = ½ mv2

Principle of conservation of energy

Energy cannot be created or destroyed but can be change from one form to another

Power

Rate of doing work

Power = work done / time taken

P = force x distance / t d/t = v

P = Fv In watts (W)

Efficiency

Is the ratio of useful energy output to total energy input

Efficiency = useful power output / total power input

X100 for percentage

Energy conservation

The act of reducing energy consumption

Energy efficiency

Is defined as any product or process that makes it possible to enjoy the same standard of living while using less energy

Current

The rate at which charged particles pass a point in a circuit

I = Q/t

I = current ampere (A)

Q = charge. Coulomb (C)

I = Ne/t

N = number of electrons

e = single electron 1.6×10-19C

Potential difference

The electrical energy converted per coulomb of charge passing between two points

V= W/Q

V = p.d volts (V)

Electromotive force EMF

EMF of a battery is defined as the (chemical) energy converted to electrical energy when 1 coulomb of charge passes through it

E = W divided Q

E = emf W=electrical energy in joules

Q= charge in coulombs

A volt

Defined as a joule pet coulomb ( later see a watt per ampere)

Electrical power

The rate at which electrical energy is converted into other forms of energy by a circuit or a component such as a resistor in a circuit

W/t=QV/t=IV

P=IV. P= power (W) I=current (A)

V= pd in (V)

V=P/I so watts per ampere

Power (equations)

1 watt = 1 joule per second

P= VI

P= W/t

P= I2R. I is squared

Resistance

The ratio of the pd between two points to the current passing through those points

1 ohm = 1 volt per amp

V = IR. R=V/I

Ohm’s law

States that the current through a metallic conductor is directly proportional to the applied pd provided the temperature is constant

Ohmic

When the current flowing through a material is directly proportional to the applied pd across it

EG cooper wire constant temp

Non ohmic

When the current flowing through a materials is NOT directly proportional to the pd across it

EG filament lamp

Diode

Semiconductor device which has low resistance to current in one direction and high resistance in the other

Thermistors

Negative temperature coefficient (ntc) thermistor therefore resistance decreases as it heats up

Resistivity

Is equal to the resistance of a 1m length of material with a CSA (cross sectional area) 1m2

R=pL/A

L = length (m) A= area (m2) R= resistance (ohms) p= Resistivity (ohms m)

Resistivity graphs length and cross sectional area

Graph : resistance against length is directly proportional

Super conductivity

Loses all its electrical resistivity to become a perfect conductor when it’s below the critical temperature

( resistance is zero when below critical temperature)

Used in MRI (Magnetic resonance imaging) scanners and maglev train

Internal resistance

Opposite to current flow within the cell

E= V+Ir. E= IR+Ir as V=IR

E= emf of the cell

PD = EMF - Lost volts

Experiment to find internal resistance of a cell

Potential divider circuit

Vout=R1Vin/R1+R2

Heater circuit

Lighting circuit