Our Dynamic Universe Flashcards
What sign does motion going up or to the right have?
Positive
What sign does motion going down or to the left have?
Negative
In a velocity-time graph, what does it mean when the graph crosses the x-axis?
The motion has changed direction
In a velocity-time graph, how do you find the displacement of the object?
Area under the graph
In a velocity-time graph, how do you find the acceleration?
Acceleration = gradient of graph
How do you identify an acceleration-time graph?
Only has horizontal lines
In a displacement-time graph, what do horizontal lines mean?
The object is stationary
In displacement-time graphs, what does a positive gradient (upward slope) mean?
The object is moving away from the starting point
In displacement-time graphs, what does a negative gradient (downwards slope) mean?
The object is moving in the opposite direction (usually back towards the starting point)
In displacement-time graphs, what does it mean if the graph crosses the x-axis?
The displacement is overall negative
Has went left/down from the start point further than its gone forward
What equipment is required to measure acceleration?
- Slope
- Two light gates
- Timer
In a graph of a bouncing ball, why does the graph gets smaller?
Energy is being lost to the surroundings
How do you connect vectors?
Nose to Tail
If using trigonometry, where should the angle be read from?
North
How do you resolve vectors (find the horizontal and vertical components) and how do you remember which is which?
horizontal = a x cos x theta vertical = a x sin x theta
Horizontal goes a cos (across)
Vertical goes to the sin (sky)
When an object is on a slope, how do you calculate the force on the object?
How do you remember which is which?
Have a force acting parallel to the slope, and a force acting perpendicular to the slope
Fpara = mg sin theta
Fperp = mg cos theta
- mg = W*
- F = W sin theta* F = W cos theta
‘Live long and cos per’
How do you work out the unbalance force acting on an object parallel to a slope?
Fu = Fpara - Friction Fu = Wpara - Friction
What is the general affect of friction?
Slows objects down
What is the Law of Conservation of Energy?
Energy cannot be created or destroyed, only changed from one form to another
How do you find out if energy had been conserved?
Find out the energy lost (for a ball, Ep = mgh)
Find out the energy gained (Ek = 1/2 mv^2)
mass can be cancelled out if appears on both sides
Say whether or not the two values are equal
If they are, the energy has been conserved
If not, energy has been lost
How can you find out the velocity of an object?
v = d t
v = u + a t
v^2 = u^2 + 2 a s
Conservation of energy
What is Newton’s first law of motion?
If the forces acting on an object are balanced, then the object will remain at a constant velocity
What is Newton’s second law of motion?
If the forces acting on an object are unbalanced, the object will accelerate
When does terminal velocity occur, and what is it?
Occurs when air resistance = weight of the object (balanced forces)
Constant velocity - no acceleration
What increases when velocity increases?
Friction
Air resistance
What is the equation related to Newtons second law?
Fu = m a
How do connected systems accelerate?
At the same rate
a = Fu / m
How do you work out the force acting on a connected system?
F = total pulling force - total friction
How would you find the tension in the coupling between two objects in a connected system?
Look at the coupling at what it is pulling, ignore anything before it
Tension - Friction of object = mass of object x acceleration of system
T - Fr = m a
Change side, change sign for Fr
What is the symbol for momentum?
p
How do you calculate momentum?
p = m v
What is the Law of Conservation of Linear Momentum?
In the absence of external forces, the total momentum just before a collision/explosion is equal to the total momentum just after the collision/explosion
What is the unit for momentum (p)?
kg ms-1
kilograms per metre per second
What happens during inelastic collisions?
Objects stick together after colliding
Energy is lost
Ek before > Ek after
What is the equation for inelastic collisions?
m1v1 + m2v2 = m3v3
What happens during elastic collisions?
Object bounce apart after colliding
Energy is conserved
Ek before = Ek after
What is the equation for elastic collisions?
m1u1 + m2u2 = m1v1 + m2v2
Remember directions in collision questions
How do you show whether a collision is elastic or inelastic?
Work out the total kinetic energy before the collision
Work out the total kinetic energy after the collision
‘Total kinetic before the collision (!)= total kinetic energy after the collision, therefore the collision is ______’
What are the key characteristics of an explosion?
Starts with one object, splits into two
m1v1 = m2v2 + m3v3
Momentum is conserved (total p before collision = total p after collision)
Kinetic energy increases - no kinetic energy at start (stationary)
What is Newton’s third law of motion?
If A exerts a force on B, B exerts an equal but opposite force on A
What is the symbol for impulse?
Ft
How do you calculate impulse?
Ft = mv - mu
Ft = m (v - u)
Area under a Force-Time graph
What is the unit for Impulse?
Ns
Newton seconds
What does it mean if a force-time graph has a high force over a small period of time?
Object is colliding with a hard surface
High force, little time
What does it mean if a force-time graph has a low curve over a long period of time?
Object is colliding with a soft surface
Increased surface contact time
What are the purpose of crumple zones?
Increase the contact time, this reducing the force
Describe an experiment to measure gravitation.
Drop an object from a known height
Time how it takes to hit the ground accurately
Use s = ut + 1/2at to calculate the acceleration
a = g
How do you calculate horizontal displacement?
horizontal displacement = horizontal velocity multiplied by time
sh = vh x t
Key points about horizontal motion
Horizontal velocity remains constant
As horizontal velocity increases, the horizontal distance (range) travelled also increases.
No acceleration
Sh = vh x t
Area under horizontal velocity-time graph = horizontal displacement
What are the key points of vertical motion?
Initial velocity = 0ms
Acceleration = -9.8ms
Can use v = u + at , s = ut + 1/2at^2 , v^2 = u^2 + 2as
Area under vertical velocity-time graph - vertical displacement
If fired from ground and lands on ground, sv = 0m
How do you draw a SUVAT table?
three columns SUVAT down first Horizontal along top Vertical along top Black out v and a for horizontal column Fill
Key Projectiles info
Constant horizontal motion
Constant vertical acceleration
How do satellites orbit planets/stars?
Free fall
High horizontal velocity
Gravitational pull
Path follows the curvature of the planet/star
Why to astronauts in satellites seem weightless?
Constantly falling at same rate the satellite is falling
What caused the formation of suns, planets and solar systems?
Gravity
What is a field?
A place where a force is exerted on a particle of mass
What does ‘Gravitational field strength’ mean?
The gravitational force acting on a unit of mass at a point
How do you calculate gravitational field strength?
g = F / m
g measured in Nkg-1
What was Newton’s law of gravitation?
Every body with mass will exert a force on every other body with a mass.
How do you calculate the gravitational force between objects?
Gravitational Force is equal to the Gravitational Constant times the two masses, all divided by the distance between to the two objects squared
F = (G m1 m2) / r^2
What is the gravitational constant?
6.67 x10^-11 Nm^2kg-2
Found in data booklet
What is r the distance of in terms of Gravitation?
Distance between two object
Make sure that it is measured from centre to centre of objects
What are inertial reference frames?
Places that are moving at constant speeds relative to each other
When is the speed of light the same for all observers?
In a vacuum
What symbols are used to convey proper time and proper length?
t and l
These are the real measurement when stationary or moving within the same reference frame
What symbols are used to convey dilated time and contracted length?
t’ and l’
This is what is observed by an observer
v^2 / c^2 = ?
c^2
When do time dilation and length contraction occur?
When an object approaches light speed
The contracted length will always be less than the actual length
The dilated time will always be greater than the actual time
What is the Doppler Effect?
The change of frequency observed when the source of the sound is in motion
What happens to the frequency of a sound when the source is moving towards to the observer?
Frequency increases
What happens to the frequency of a sound when the source is moving away from the observer?
Frequency decreases
In the Doppler Effect equation, what sign do you use if the source if moving towards the observer?
Negative
In the Doppler Effect equation, what sign do you use if the source if moving away from the observer?
Positive
When does blueshift occur?
When the source is coming towards the observer
When does redshift occur?
When the source is moving away from the observer
If a source is moving towards an observer, what happens?
Shorter wavelength Higher frequency Blueshift Use negative sign (Blue is a sad colour)
If a source is moving away from an observer, what happens?
Longer wavelength
Lower frequency
Red shift
Use positive sign
How do you calculate red shift?
z = v/c
red shift = velocity / speed of light
z = observed wavelength - resting wavelength / resting wavelength
What is Hubble’s Law?
The further away a galaxy is, the faster it is travelling
v = Hod
velocity = Hubble’s constant x distance to galaxy
How would you calculate the age of the universe?
d = v t , v = Ho d
d = Ho d t
Rearrange
What is dark matter?
The missing matter that holds our universe together
Controls rate of rotation
Can’t see it
What is dark energy?
Causes the acceleration of the expanding universe
As the temperature of a star increases….
There is a greater intensity of radiation at each wavelength (more radiation)
The peak wavelength decreases
Graph moves higher and to the left as the temperature of stars increase
What evidence is there to the Big Bang Theory?
Cosmic Background Microwave Radiation
Olber’s Paradox
Abundance of lighter elements (H, He)
Red shift of galaxies (moving away)
What is Olber’s Paradox?
If there are stars in the sky that give light, why is the sky dark?
What is a resultant force?
The vector sum of all the forces acting on an object
What are the three types of uncertainties?
Systematic
Random
Reading
What are systematic uncertainties?
When all the measurements are affected in the same way
Can be a mistake in apparatus or how the measurement is carried out
e.g. measuring with a ruler from the end rather than the 0 mark
e.g. ignoring friction in an experiment
What are random uncertainties?
When the results don’t exactly match up
Can do an estimate to find the true value.
How do you write a random uncertainty?
Average value calculated +/- uncertainty
What are reading uncertainties?
How well a scale can be read/how accurate it is
What is an analogue scale?
Rulers, etc
How do you calculate the reading uncertainty on an analogue scale?
+/- half of the smallest division on the scale
e.g. for a ruler - smallest division = 0.1cm - uncertainty = +/- 0.05cm
What is a digital scale?
Something that displays the measurement
e.g. set of electronic scales
How do you calculate the reading uncertainty on digital scales?
+/- 1 of the smallest division presented
e.g. timer - 0.00s - uncertainty - +/- 0.01s
How do you find the percentage uncertainty?
%error = calculated uncertainty / measurement taken x 100
Why would you find a percentage uncertainty?
To compare uncertainties
In an elevator, when is the reading on the scales equal to the persons weight?
When the lift is stationary or travelling at a constant velocity
In an elevator, when would the scales display a greater weight than the person, and how would you find this out through calculation?
When lift is accelerating upwards or decelerating downwards
Calculate persons weight
Work out the Unbalanced Force, m being the weight of the person
Reading = Fu + Weight of the person
In an elevator, when would the reading on the scales be less than the person’s weight? How would you find out the value on the scales?
When lift is accelerating downwards or decelerating upwards
Calculate persons weight
Find unbalanced force, m being the weight of the person
Reading = W - Fu
If the horizontal velocity is 40ms and the vertical velocity has a final value of 30ms downwards. what is the final speed of a ball?
10ms
How can the mass of a galaxy be estimated?
By the orbital speed of stars within the galaxy
A spacecraft is travelling at 0·10c relative to a star.
An observer on the spacecraft measures the speed of light emitted by the star to be….?
1c
A person stands on a weighing machine in a lift. When the lift is at rest, the reading on the weighing machine is 700N.
The lift now descends and its speed increases at a constant rate.
What is the reading on the weighing machine?
A constant value less than 700N
How would you find out the height above the ground at which an object land?
Use s = ut +1/2 at^2
where s = height
u = initial vertical velocity
a = -9.8
