Unit 3 Flashcards
What is a scalor quantity
Quantity with size only
Give some examples of scalor quantities
Distance, speed, time, mass, energy, power, temperature
What is a vector quantity
Quantities with magnitude and direction
Give some examples of vector quantities
Displacement, velocity, acceleration, force, weight, momentum
How is magnitude and direction found from a vector diagram
Magnitude - Pythagoras
Direction - trigonometry (SOH-CAH-TOA)
How is velocity of a horizontal vector found
Vcos0
How is force of a vertical vector found
Fsin0
What angle is always used when finding rectangular components of vectors
Angle to the horizontal
When displacement is constant, what do the velocity and acceleration graphs look like?
Both are a straight line at 0 a long the x-axis
When velocity is constant what happens to the displacement on a motion-time graph
Increases
When there is a constant positive acceleration, what does the displacement - time graph look like
Smooth increasing curve ( _/ ) ➡️↗️
When there is a constant positive acceleration what happens to velocity
Velocity increases from zero upwards
When there is a constant negative acceleration what happens to the displacement
Smooth upwards curve ( ↗️➡️ )
How could displacement be found from a velocity-time graph
Area under graph
How could acceleration be found from a velocity-time graph
Gradient of line
How would velocity be found from a velocity time graph
Value from best fit line
How would displacement be found from a displacement-time graph
Value from best fit line
How would velocity be calculated from a displacement-time graph
Gradient of line
How would acceleration be found from a displacement-time graph
Calculate from velocity values, a = v-u/t
What indicates a change in direction on a velocity-time graph
Crossing the x-axis
Define acceleration
Change in velocity per second
From the equation a + v-u/t what does the u and v represent
u = starting velocity v = final velocity
What experiment can be used to find the acceleration of an object
Measured using a trolley with a mask(s) and light gate (s)
What measurements would need to be made when measuring acceleration
- length of mask
- time through light gate(s)
- time between light gates or time between masks
What is Newton’s first law of motion
An object will remain at rest or continue in at a constant speed unless acted on by an unbalanced force
What is Newton’s second law
An unbalanced force will cause an object to accelerate
In what direction does friction act relative to the object
In the opposite direction
How can the unbalanced force be calculated
F = Fh - Ffric
What is tension
The pulling force acting on a cable
When a lift is stationary or moving at a constant speed are the forces balanced or unbalanced
Balanced
When are the forces unbalanced in a lift
When the lift is accelerating or decelerating
When is the value for ‘a’ in the equation T = mg + ma positive
Accelerating up or decelerating down
When is the value for ‘a’ negative
Accelerating down or decelerating up
In the rocket example of vertical thrust when are the forces balanced
When rocket is stationary
Why does a rocket acceleration increase
Mass decreases - fuel used up
Weight decreases - acceleration due to gravity decreases
Air less dense - air resistance decreases
How is Wpara calculated
Wpara = mgsin(angle)
How is Wperp calculated
Wperp = mgcos(angle)
How is the force calculated if the object is moving up a slope
F = Wpara - Ffric
When is the equation F = Wpara + Ffric used
When an object is moving up the slope
Define work done
Amount of energy transferred from one place to another
What is power
The amount of energy transferred per second
If no friction acts on a slope how does the energy at the top and bottom compare
Ep at top = Ek at bottom
If friction acts on a slope how does the energy at the top and bottom compare
Ep at top > Ek at bottom
Is friction acts on a slope how would the potential energy be found
Ep = Ek at bottom + friction (Ew)
What is momentum
The product of an objects mass and velocity
What is the conservation of linear momentum
The total momentum before an interaction us equal to the total momentum after an interaction, in the absence of net external forces
How is total momentum found
m1u1 = m2u2
How is momentum calculated in a nonstick collision
m1u1 + m2u2 = m1v1 + m2v2
How is momentum calculated in a sticking collision
m1u1 + m2u2 = (m1 + m2) v
How is momentum calculated in an explosion
(m1 + m2) u = m1v1 + m2v2
In what type of collision is energy conserved
Elastic collision
What does the term ‘energy conserved’ mean
Ek total before = Ek total after
In what type of reaction is energy not conserved
Inelastic collision
How is kinetic energy calculated
Ek = 0.5 m1u1^2 + 0.5 m2u2^2
What is impulse
The change in momentum
What is impulse measured in
Ns
What needs to be taken into account when calculating impulse
Direction of the velocities and force
On an impulse graph, how does a hard surface compare to a soft surface
Hard surface - high force, short time
Soft surface - small force, long time
How can impulse (Ft) be calculated from a graph
Ft = 1/2 bh
Area under graph
What is needed to measure contact time
A fast timer
What is a projectile
Objects moving under their own interia and so only affected by the force of gravity
What is interia
An objects resistance to change
What are the requirements for a projectile
- constant horizontal velocity
- constant vertical acceleration
For a full projection how is the horizontal velocity calculated
Uh = vcos(angle)
For a full projection how is the vertical velocity calculated
Uv = vsin(angle)
What is gravitational attraction between two objects directly proportional to
The mass of each object
What is gravitational attraction inversely proportional to
The square of the objects separation
What decreases as you move away from a planet’s surface
Gravitational field strength of a planet
Why do occupants of a space shuttle appear weightless
Occupants are accelerating towards the earth at the same rate as the space shuttle making them appear weightless
What are the two postulates for special relativity
- laws of physics are the same for all observers
- speed of light the same for all observers
In the time dilation equation what does ‘t’ represent
Time interval for moving observer
In the time dilation equation what does ‘t^1’ represent
Time interval for a stationary observer
Is time interval for a stationary observer longer or shorter than that experienced by a moving observer
Time interval longer for stationary observer
What is length contraction
The muons are considered to be moving a different distance in the same amount of time
For length contraction, what observer experiences the shortest distance
Stationary observer
What does the Doppler effect show
Shows how the detected frequency from a source can change depending on the relative motion between the source and the observer
What happens to the frequency of the waves as the source approaches
Frequency increases, more waves detected per second
As the source moves away what happen to the frequency of the source
Frequency decreases, less waves detected per second
Using the Doppler effect equation, what sign is used when the source is moving towards an observer
Negative (-)
Using the Doppler effect equation, what sign is used when the source is moving away from an observer
Positive (+)
What is Doppler redshift
Occurs when the light the light from an object that is moving away from us is ‘shifted’ towards the longer wavelength end
What does a larger redshift tell us about a galaxy
Galaxy is moving away from us at a faster rate
What happens to the wavelengths of light if an object is moving towards us
Blueshifted
What did the galaxy form from
A large cloud of dust and gas called a nebula
What attracted the small particles together
Electromagnetism
What were the larger clumps attracted by
Force of gravity
What evidence is there for the expanding universe theory
- darkness of night sky
- redshirt of most galaxies
- abundance of light elements
- cosmic microwave background radiation (CMBR)
Are more distant galaxies moving away from us at a faster or slower rate than nearby galaxies
Faster
What is dark matter
From of matter that doesn’t emit radiation in the electromagnetic spectrum
What does dark matter help to explain
Galaxies are revolving at a faster rate than predictions suggest
What is the calculated amount of dark matter not enough to stop
The expansion of the universe
What is dark energy
The unknown force that acts against the force of gravity
What does dark energy cause
Causes the expansion of the universe to accelerate
Is the rate of expansion of universe increasing or decreasing
Increasing
What are distant galaxies driven apart by
Dark energy
What is the colour of a star related to
It’s temperature
What colour are hotter stars
Blue
What colour are cooler stars
Red
What are the properties of hotter stars relating to the radiation spectrum
- short wavelength
- high frequency
- high peak
- large area of graph
What are the properties of cooler stars relating to the radiation spectrum
- long wavelength
- low frequency
- low peak
- small area of graph
What is the peak wavelength of a star is inversely proportional to
It’s surface temperature
What is the surface temperature of a star directly proportional to
Peak frequency of a star
As the star gets hotter what happens to the energy emitted per second
Higher energy emitted per second
