Flashcards in Unit 1 - Our Dynamic Universe Deck (103):
What is a scaler 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?
Direction -trigonometry (SOH-CAH-TOA)
How is velocity of a horizontal vector found?
How is force of a vertical vector found?
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 along the x-axis.
When velocity is constant what happens to the displacement on a motion-time graph?
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.
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?
When are the forces unbalanced in a lift?
When the lift is accelerating or decelerating.
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.
When is the value for 'a' in the equation T = mg + ma positive?
Accelerating up or decelerating down.
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
As 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 is 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 = (ml + m2) v
How is momentum calculated in an explosion?
(ml + m2) u = m1v1 + m2v2
In what type of collision is energy conserved?
What does the term 'energy conserved' mean?
Ek total before = Ek total after
In what type of reaction is energy not conserved?
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?
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^l' 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?
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?
Using the Doppler effect equation, what sign is used when the source is moving away from an observer?
What is Doppler redshift?
Occurs when 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 that is moving towards us?
Where did the galaxy come from?
A large cloud of dust and gas called nebula.
What attracted the smaller particles together?
What were the larger clumps attracted by?
Force of gravity.
What evidence is there for the expanding universe theory?
- Darkness of night sky.
- Redshift of most galaxies.
- Abundance of light elements.
- Cosmic Microwave Background Radiation (CMBR)
What colour are hotter stars?
Are more distant galaxies moving away from us at a faster or slower rate than nearby galaxies?
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?
What are distant galaxies driven apart by?
What is the colour of a star related to?
What colour are cooler stars?
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.