Forces/motion Pt2: Momentum/ Moments/astrophysics Flashcards
What three things can change an objects momentum
- mass
- if it accelerates or decelerates
- direction
A car of mass 1000kg travels at a velocity of 20m/s and collides with a stationary motorbike of mass 500 kg. The vehicles move together after impact. Calculate their velocity
Momentum is conserved Momentum before = momentum after (1000x20) +(500x0) = (1000+500) v 20000 = 1500v 20000/1500 1=V
What is equal to rate of change of momentum?
Force
How can you reduce the impact of collision (in terms of collision time and force and momentum)
Force is equal to the rate of change of momentum, so the impact of force on a vehicle can be reduced by increasing collision time
What are three things that cars have to increase collision time
Airbags
Crumple zones
Seat belts
How does a crumple zone reduce force?
It absorbs the energy from the impact force, thus increasing the collision time
So change in momentum is gradual
What are the two functions of a seatbelt in car crashes
- stops you from colliding with the interior of the vehicle
- stretchy, so increases the time taken for passengers momentum to reach 0
What is the use of an airbag in a collision
-it is compressible so increases the time taken for momentum to reach 0
Definition of a moment
The turning effect of a force about a pivot
Equation for a moment
M=FD
What are the units for a moment
NM
Equation for momentum
P=MV
Describe the clockwise and anti clockwise moments if an object is balanced
The total clockwise moment will equal the total antilock wise moment
Where is the center of gravity located for a symmetrical object with uniform density?
At the point of symmetry
What two variables do you need for an object to be stable and to not topple
Low center of mass
Wide base
What is a galaxy
A large collection of billions of stars
What is weight
The force acting on an object due to gravitational attraction
What is the gravitational field strength like on a planet all the way around
It is roughly the same
What is the gravitational field strength of the gas planets in comparison to the earth (Saturn, Neptune, Uranus)
More than the earth
What do asteroids and comets orbit around
The sun
What are two similarities that every orbit has
The same plane
The same direction
What are three differences that every orbit has
Distance from the sun
Speed it travels
Time taken
Planets furthest away front the sun take the.. amount of time to travel so have the …. Speed
Furthest
Slowest
Describe the shape of the orbits of these three bodies:
Planet
Moon
Comet
Moon is circular
Planets are slightly eliptical
Comets are highly elliptical
Why does a comets speed change
Because it’s orbit is elliptical
and is different distances away from the sun so different gravitational attractions
What does time period mean in terms of orbits
The time taken to complete one orbit
State the equation for orbital period with units
V(m/s)= 2piR(m)/ T(s)
What is the orbital radius
The distance form the center of the earth to the orbit
Not from the surface if the earth
The Hubble Space Telescope moves in a circular orbit. Its distance above the Earth’s surface is 560 km and the radius of the Earth is 6400 km. It completes one orbit in 96 minutes.
Calculate its orbital speed in m/s.
1) total radius = 560km+ 6400km = 6960km
2)6960km=6960000m
3) 6960000 x 2 x Pi=43730969.74
4) divided by (96x60 = 5760s)
= 7590 m/s
Formula for weight with units
Weight(N) = mass (kg) x gravitational field strength (n/kg)
What two factors affect the size of a force between two bodies
Mass
Distance between the masses
If the distance between two masses is doubled, then what happens to the forces between them
They are quartered (inverse square law)
Why do planets closer to the sun have more of a circular orbit
Because they have the greatest gravitational attraction
Star classification:
O B A F G K M
Name the star spectrum in order of colors
O= blue B= blueish white A= white F=yellow white G= yellow K=Orange M= Red
Two factors that affect star brightness of a star
- how far away it is(distance)
- energy released per second(luminosity)
Explain why larger stars have more energy
Larger stars have more energy because they have a greater surface area
Apparent magnitude meaning
How bright a star is from the earth
Absolute magnitude meaning
Brightness of a star from equal distance to all other stars
What are three ways that astronomers describe the brightness of a star in
- apparent brightness
- absolute brightness
- luminosity
Explain the formation of a star, with similar mass to the sun
1-)Gravitational forces pull hydrogen and dust particles together.
And this cloud of dust is called a nebulae
2-)As more material is gathered, gravitational forces become stronger
and the temperature increases, so this contracting cloud of gas is called a protostar
3- as gravitational forces continue to increase,
the temperature increase even more,
so hydrogen begins to form helium through nuclear reaction
This energy from the nuclear reaction creates forces
That causes the gases to expand
Eventually the outwards forces are equal to the inwards gravitational forces and the star is in its stable state
Main sequence star
4-)yet as hydrogen nuclei begin to decrease,
gravitational forces begin to compress together
Where energy from this causes gases to expand and cool
Called a red giant
5-) hydrogen nuclei are no longer available so nuclear reactions stop
And outer layer is cast off
This is called a planetary nebula
6-) after some time helium fusion reactions begin
And gravitational forces begin to compress
Temperature increases and so the colour changes to white
This is called a white dwarf
7-) when the white dwarf cools it is called a black dwarf
Explain the formation of a star greater than the sun
1-)Gravitational forces pull hydrogen and dust particles together.
Nuclear reactions have begun and a nebula is formed
2-)As more material is gathered, gravitational forces become stronger
and the temperature increases, the star in this phase is called a protostar
3-)Nuclear reactions cause hydrogen nuclei to form into helium,
and High temperatures create forces that cause gases to expand outwards.
These forces balance with the inward gravitational forces
and the star is now called a main sequence star
4-)yet as hydrogen nuclei begin to decrease,
gravitational forces begin to compress together and the core shrinks
So there is an increase in temperature
Where energy from this causes gases to expand and cool
Called a large red supergiant
5-) Runs out of nuclear fuel and the core begins to collapse
So explodes to create a supernova
6) Any remaining matter from this explosion forms a dense neutron star
7) or then some large stars will continue to collapse under the force of gravity until it forms a black hole
And a black hole is so dense that not even light can escape
Draw the hertsprung russel diagram
Luminosity/ absolute magnitude on the y axis(goung from dimmest to brightest)
Temperature on the x axis(going from hottest to coolest
Main sequence stars in the middle
White dwarfs in bottom left
Large super giants at the top
Underneath that should be giants
What are two pieces of evidence for the Big Bang?
Galactic red shift
And cosmic microwave radiation
Describe what the frequency of waves is like and the wavefronts when an object is stationary
The frequency of waves is emitted at a constant frequency
And the wavefronts are symmetrical
Describe the redshift of more distant galaxies and describe the frequency of the waves and their speed
has a much larger redshift
As frequency of waves has increased
and travels much faster
(Rmeber that red travels faster than violet)
Explain how scientists know that the universe is expanding in terms of galaxies
Because more distant galaxies are moving faster than closer galaxies
What does the Big Bang theory describe
That the universe began from a small region that was very hot and dense and has been expanding since
What is dark energy
Matter and energy that you cannot detect
Explain how cosmic microwave background radiation supports the theory of the Big Bang
Scientists have discovered that there is microwave radiation coming in all directions of the universe, which have long wave lengths and Low frequencies, suggesting that the universe expands
Where is the light spectrum found in space
In supernovae
The faster an object is moving the…… the frequency
Greater
Describe frequency of a car as it is close to you
Frequency is high
Why does a distant galaxy emit a larger wavelength than the sun
Because it has a larger redshift so is moving further away
What is the equation for the Doppler effect
Change in wave length/ reference wave length = velocity/ speed of light(3x10^8)
name five factors that can affect braking distance
- worn out tyres
- wet or icy road
- reaction time
- mass of the car
- how fast it is traveling
Name three factors that can affect thinking distance
- under the influence of drugs or alcohol
- being tired
- being distracted
When one heavy object and one light object push away from each other, why do they have different
velocities but the same momentum
Momentum before and after a collision is always the same in a closed system
because momentum is conserved
But acceleration will be different because the heavy object and light object have different masses
And according to Newton’s second law of motion, the acceleration depends on the mass (F=MA)
Do two objects with different masses exert a force of same size on each other during collision? Yes or no and explain why
They do exert a same force on each other because of Newton’s third law,
where he states that every action has an opposite and equal reaction,
So the magnitude of the forces will be the same
When a skier falls down a hill, why is he not severely injured? Use the ides of forces and momentum to explain
The time taken to fall is long so there is a gradual decrease in momentum so the force applied is less
Suggest why some aircraft need a big landing space to land safely (2)
Because they may have a large mass or large velocity so will therefore have a larger momentum
So increasing space increases braking time
Why would a plane without a parachute have a longer stopping distance and why
Longer braking time Because there will be less air resistance so will take more time to decelerate
If 7N is needed to turn a lever with a distance of 0.04 from the pivot, why does a lever with distance 0.02 need more force
Because smaller distance needs more force FOR THE SAME MOMENT
State a difference between the orbit of a planet and the orbit of a moon
A planet orbits around a star
A moon orbits a planet
Why do planets closer to a star take less time to orbit (2)
Because they have smaller orbital paths (think about an orbit and how it is shorter next to the sun)
And the gravitational pull of the sun is stronger
A vehicle is sent into space but there is a possibility that it can collide with rocks. Suggest why scientists give it a low speed
- so that it has a less momentum so less damage
- and so that scientists have time to monitor it
Explain why the distance between two planets can vary
Eg: how one planet can be on one side of sun and other can be on other side
Because they both have different orbital periods, so will be at different motions, for example they might be t opposite sides of the sun
Why will two objects on Mars fall at the same rate
Because there is no air resistance
If a star has a large mass, will it spend more time in the main sequence or less and explain why?
Less time because the hydrogen fuel will burn faster
Explain How can you find the centre of mass for an irregular shaped object
1)draw the point of suspension and suspend from that point, and suspend a plumb line for the same point, and wait until it stops moving
2)draw a line down the plumb line
3)suspend from another point with a plumb line and draw another line
4)the centre of gravity will be where the both lines intersect
Explain why a freely suspended object swings, in terms of moments and centre of mass
The centre of gravity of the object acts at a distance from the suspension point (the pivot)
So this creates a moment about the pivot
So this moment causes it to swing
So that the centre of gravity will act directly below the suspension point
