physics exam revsion
forces
When a force acts on an object, the object may change shape by bending, stretching or compressing (deformation)
Extension happens when an object increases in length, and compression happens when it decreases in length.
force = spring constant × extension
force (F) is measured in newtons (N)
spring constant (k) is measured in newtons per metre (N/m)
extension (e), or increase in length, is measured in metres (m)
limit of proportionality refers to the point beyond which Hooke's law is no longer true when stretching a material
the extension is directly proportional to the force applied.
Work is done when a spring is extended or compressed. Elastic potential energy is stored in the spring
elastic potential energy = 0.5 × spring constant × (extension)2
waves
motion
Distance is how far an object moves. It does not include an associated direction, so distance is a scalar quantity.
distance travelled = speed × time
The velocity of an object is its speed in a particular direction. Velocity is a vector quantity because it has both a magnitude and an associated direction.
Acceleration is the rate of change of velocity. It is the amount that velocity changes per unit time.
change in velocity = final velocity - initial velocity
At terminal velocity, the object moves at a steady speed in a constant direction because the resultant force acting on it is zero.
:
According to Newton's First Law, an object remains in the same state unless a resultant force acts on it. If the resultant force on an object is zero, this means:
a stationary object stays stationary
a moving object continues to move at the same velocity (at the same speed and in the same direction)
resultant force = mass × acceleration
stopping distance = thinking distance + braking distance
thinking distance is the distance a vehicle travels in the time it takes for the driver to apply the brakes after realising they need to stop
braking distance is the distance a vehicle travels in the time after the driver has applied the brake
click to edit
A driver's reaction time can be affected by:
tiredness
drugs
alcohol
distractions
When a force is applied to the brakes of a vehicle, there is work done by the friction between the brakes and the wheel. This reduces the kinetic energy of the vehicle, slowing it down and causing the temperature of the brakes to increase.
The braking distance of a vehicle can be affected by:
poor road and weather conditions, such as wet or icy roads
poor vehicle conditions, such as worn brakes or worn tyres
The faster a vehicle travels, the greater the braking force needed to stop it in a certain distance. A greater braking force produces a greater deceleration
In longitudinal waves, the vibrations are parallel to the direction of wave travel.
transverse travel perpendicular
Mechanical waves cause oscillations of particles in a solid, liquid or gas and must have a medium to travel through. Electromagnetic waves cause oscillations in electrical and magnetic fields.
parts of waves
peak - the highest point above the rest position
trough - the lowest point below the rest position
amplitude - the maximum displacement of a point of a wave from its rest position
wavelength - distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough
frequency - the number of waves passing a point each second
time period = 1/frequency
The particles move up and down as the wave is transmitted through the medium.
Examples of longitudinal waves include:
sound waves
ultrasound waves
Longitudinal waves show areas of compression and rarefaction:
compressions are regions of high pressure due to particles being close together
rarefactions are regions of low pressure due to particles being spread further apart
they move backwards and forwards between compressions as the wave is transmitted through the medium.
examples of transverse waves
-seismic waves
-ripples on surface of water
-vibrations of guitar string
Electromagnetic waves are transverse waves. Their vibrations or oscillations are changes in electrical and magnetic fields
click to edit
transfer energy as radiation from the source of the waves to an absorber
can travel through a vacuum such as in space
travel at the same speed through a vacuum or the air
Ultraviolet waves, X-rays and gamma rays are types of ionising radiation. They can add or remove electrons from molecules, producing electrically charged ions. Ionisation can have hazardous effects
ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer
x-rays and gamma rays can cause the mutation of genes, which can lead to cancer
click to edit
Background radiation is all around us, all the time. Sources include:
radioactive rocks in the Earth's crust
cosmic rays from space
man-made sources such as nuclear weapons fallout and nuclear accidents
reflection and refraction
Waves - including sound and light - can be reflected at the boundary between two different materials. The reflection of sound causes echoes.
The angles of incidence and reflection are measured between the light ray and the normal
In a virtual image, the rays appear to diverge from behind the mirror, so the image appears to come from behind the mirror.
ight waves may change direction at the boundary between two transparent materials. Refraction is the change in direction of a wave at such a boundary.
scalars and vectors
contact and non contact forces
A physical quantity is something that can be measured. Scalar quantities only have a magnitude or size.
examples: temperature,mass,speed
Vector quantities have both magnitude and an associated direction.
examples: force,displacement, velocity, acceleration, momentum
Contact forces are forces that act between two objects that are physically touching each other. friction, air resistance, tension
When a contact force acts between two objects, both objects experience the same size force, but in opposite directions.
When a contact force acts between two objects, both objects experience the same size force, but in opposite directions. electrostatic, gravitational,magnetic