physics p2 cram Flashcards
Examples of scalar quantities
Scalars : speed, distance
Examples of vector quantities
Vectors: force, acceleration
Examples of contact forces
Contact forces: friction, tension, air resistance, normal contact force
Examples of non-contact forces
Non-contact forces: gravitational, magnetic, electrostatic
What is a newton metre?
A newton meter measures weight with spring-balance
What does an object’s weight depend on?
An object’s weight depends on the gravitational field strength
What does elastic mean?
Elastic means the object returns to its original shape after all forces have been removed
What does inelastic mean?
Inelastic means the object does not return to its original shape after all forces have been removed
What happens in inelastic deformation?
In inelastic deformation, all energy is transferred to object’s elastic potential energy store
What is upthrust equal to?
Upthrust is equal to weight of liquid that has been displaced by object
What happens when an object is less dense than the liquid it is in?
When an object is less dense than the fluid, there is more upthrust and so the object will float
What happens when an object is more dense than the liquid it is in?
When an object is more dense than the fluid, there is less upthrust and so the object will sink
What is atmospheric pressure caused by?
Atmospheric pressure is created on a surface by air molecules colliding with the surface
What happens to atmospheric pressure when the height above earth increases?
Atmospheric pressure decreases when the height above earth increases because the number of air molecules increases so weight of air above surface decreases
What is displacement? (physics terms)
Displacement is a vector quantity, which is the distance of direction in a straight line from an object’s starting point to it’s finishing point
What does it mean about velocity when an object is in circular motion?
An object is in circular motion means the direction is always changing so the velocity is always changing
How do you find acceleration on a velocity-time graph?
Acceleration can be found by drawing a tangent on the curved part of a velocity-time graph
How do you find the distance travelled in a certain amount of time on a velocity-time graph?
Distance travelled in a certain time is the area under a section of the velocity-time graph
What is drag?
Drag is the frictional force caused by any fluid on a moving object
What happens to an object when the force of gravity is greater than the frictional force?
When the force of gravity is greater than the frictional force, the object accelerates and speed increases, so friction increases
What is the role of parachutes?
Parachutes increase air resistance to lower the terminal velocty
How do you calculate stopping distance?
Stopping distance = thinking distance + braking distance
What factors increase thinking distance?
Increasing distance is increased by: faster vehicle speed, slow driver reaction times
What factors increase braking distance to stop whilst brakes are applied?
Braking distance increased by: faster vehicle speed, poor road surface, wet or icy weather
What is the work done when stopping a vehicle?
Driver brakes, causing brake pads to be pressed onto wheels > friction between them causes work to be done > energy transferred from kinetic energy stores of wheels to thermal energy stores of brakes > brakes heat up
What can large deceleration cause?
Large deceleration can cause brakes to overheat and vehicle to skid
What does the conservation of momentum state?
Conservation of momentum states that in a closed system, total momentum before an event equals the total momentum after an event
What is the effect of increasing time taken for momentum to change?
By increasing the time taken for momentum to change, the force acting on the object decreases
What safety features increase time for change in momentum?
Air bags, seat belts, cushioned flooring, crash mats and bike helmets increase the time taken for momentum to change
How does air bags prevent accidents?
Air bag inflates during car crash > compressing air decreases your velocity over a longer time > rate of change of momentum is smaller > forces felt are smaller
What is the frequency of waves?
Frequency of waves is the number of complete waves passing a certain point each second
What is the period of waves?
Period is the amount of time it takes for a complete wave to pass a point
What is amplitude of waves?
Amplitude is the maximum displacement of a point on wave from its rest position
What is meant by wavelength?
Wavelength is the length of a full cycle of a wave
What can happen to a wave when it hits a boundary?
When a wave hits a boundary, it can be absorbed, transmitted or reflected
What are transverse waves?
Transverse waves are oscillations that are perpendicular to direction of energy transfer
What are the types of transverse waves?
Types of transverse waves: water ripples, em waves, waves on a string
What are longitudinal waves?
Longitudinal waves are oscillations that are parallel to direction of energy transfer
What are the types of longitudinal waves?
Types of longitudinal waves: sound waves, p-waves
What happens to rays in diffuse reflection?
In diffuse reflection, reflected rays are scattered in all direction
What happens to rays in specular reflections?
In specular reflections, reflected rays scatter in all direction
What happens when a refraction causes the wave to slow down?
When a rafraction causes the wave to slow down, the wavelength decreases and bends towards normal
What happens when a refraction causes the wave to speed up?
When a refraction causes the wave to speed up, the wavelength increases and bends away from normal
What happens to wave fronts in a refraction?
Wave fronts are closer together in a refraction as wavelength is shorter
What is meant by ‘real image’?
Real image is an image formed when light rays from a point on an object come together at another point
What is meant by ‘virtual image’?
Virtual image is an image formed when light rays appear to have come from one point, but have actually came from another
What can convex lenses produce?
Convex lenses can produce real or virtual images
What can concave lenses produce?
Concave lenses can always produce virtual images
What is focal length?
Focal length is distance between the centre of the lens and principal focus
What type of lenses are used for magnifying glasses?
Magnifying glasses use convex lenses to create a virtual image
What is the difference between how black and white objects respond to visible light?
Black objects absorb all wavelengths of light whereas white objects reflect all wavelengths of visible light equally
What happens to IR radiation when trees and surroundings are at the same temperature?
When trees and surroundings are at the same temperature, the tree absorbs IR radiation at the same rate it emits it which keeps it at a constant temperature
What happens to IR radiation when an object is colder than surroundings ie ice cream?
Cold objects ie ice cream absorbs IR radiation faster than it emits it, which increases its temperature
What is perfect black body?
Perfect black body is an object that absorbs all radiation that hits it
What is the difference of radiation emmition at daytime and at nighttime?
At daytime, earth absorbs more radiation than it emits so temperature increases. However at nighttime, earth emits more radiation than it absorbs so temperature decreases
How do sound waves travel from a vibrating object?
From a vibrating object, sound waves travel as a series of compressions and rarefactions through air, which eventually hit a solid and cause the particles in solid to vibrate
What happens when a sound waves enter denser material?
When sound waves enter denser material, wavelength increases, frequency stays the same and wave speed increases
How do sound wavels travel through the ear to allow us to heat sound?
Sound waves reach air > causes ear drum to vibrate > vibrations causes other parts of ear to vibrate allowing us to hear the sound waves
What are the difference between the seismic waves P-waves and S-waves?
P-waves : longitudinal, travels through solids and liquids, faster in solids than liquids, passes through core and are detected here
S-waves: transverse waves, can’t travel through liquids, don’t pass through core and aren’t detected here
Lifecycle of a star
Lifecycle of a star:
-Dust and gas cloud (nebula)
-Gravity pulls dust and gas together
-Protostar formed
-Star gets denser, temperature rises
-Hydrogen fusion starts = outward pressure from fusion balanced inward force of gravity
-Main sequence star formed
-Hydrogen nuclei run out and star fuses with heavier elements upto iron
stars bigger than sun > red super giant > super nova > smaller stars = neutron star, massive star = black hold
or
stars same size as sun > red giant > white dwarf > black dwarf
What do supernovae do?
Supernovae eject elements, spreading them throughout the universe, where they can form new plants and stars
What happens in circular orbits?
In circular orbits, gravitational force keeps the planets and satellites in the circular orbits. It causes the object’s direction to constantly change which means the velocity is constantly changing (speed remains constant)
What happens in stable orbits?
In stable orbits, the radius of orbit changes when the speed of an object changes. Smaller radius = faster object must travel
What is red-shift?
Red-shift is the observed increase in the wavelength of light (light is fhisfted towards the rend end of the specturm). Observed when a galaxy moves away from earth. Provides evidence for big bgang theory as it shows the universe expanding.
The more distant the galaxy…
…the faster it moves away from us and the greater its red-shift
What are the steps to investigating refraction? (practical)
Steps to investigating refraction:
1) trace around block, trace incident ray and mark where light emerges from block
2) remove block and join incident ray and emerging point with straight line
3) draw normal and measure angle of incidence and angle of refraction
4) repeat with different materials, keeping angle of incidence the same
What are the steps to investigating reflection? (practical)
Steps to investigating reflection:
1) trace incident and reflected ray
2) draw normal and measure angle of incidence and angle of reflection
3) repeat with different objects
What are the differences between the reflections of smooth and rough surfaces?
Smooth surfaces give clear reflections (thin, bright reflected rays) whereas rough surfaces causes diffuse reflection (wider, dimmer reflected rays)
