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SA H Physics > Our Dynamic Universe > Flashcards

Our Dynamic Universe Flashcards

1
Q

What is the difference between a vector and a scalar?

A

Scalar requires size / magnitude only Vector requires size / magnitude and a direction

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2
Q

Which of the following are scalars? Time, Momentum, Acceleration, Energy, Speed, Velocity, Displacement, Distance, Force

A

Scalars: Time, Energy, Speed, Distance

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3
Q

Which of the following are vectors? Mass, Weight, Momentum, Impulse, Work, Temperature, Acceleration, Velocity, Speed

A

Vectors: Weight, Momentum, Impulse, Acceleration, Velocity

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4
Q

What is the difference between distance and displacement?

A

Distance is the length of the actual path travelled, Displacement is the straight line distance between where you started and where you finished, with a direction.

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5
Q

What is the difference between speed and velocity?

A

Speed is distance divided by time OR rate of chage of distance Velocity is the displacement divided by time OR rate of change of displacement, with a direction

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6
Q

What is speed?

A

Rate of change of distance

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7
Q

What is velocity?

A

Rate of change of displacement

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8
Q

What is acceleration?

A

Rate of change of velocity OR change in velocity per second.

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9
Q

What is calculated from the area under a speed-time graph?

A

Distance travelled

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10
Q

What is calculated from the area under a velocity - time graph?

A

Displacement

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11
Q

What causes a projectile to follow a curved path?

A

The projectile has a constant horizontal velocity and a constant vertical acceleration due to the gravitational field strength.

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12
Q

Explain how a satellite remains in orbit.

A

The satellite has a constant horizontal velocity and a constant vertical acceleration due to the gravitational field strength. The planet curves away from the satellite as it falls.

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13
Q

Explain how an object reaches it’s terminal velocity.

A

The weight of the object acts down towards the surface of the planet. As the object falls it accelerates, as it does this the air resistance up the way will increase as it falls faster. Eventually the weight = air resistance. This gives equal and opposite forces so the forces are balanced. This gives a constant velocity, terminal velocity.

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14
Q

What is Newtons First Law?

A

If balanced forces act on an object it will : Remain at rest or continue to travel at a constant velocity in a straight line

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15
Q

What is Newtons Second Law?

A

When an unbalanced force acts on an object it will accelerate.

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16
Q

What is the definition for 1 Newton?

A

One newton is defined as the force required to make a 1kg object accelerate at 1ms-2.

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17
Q

What is gravitational field strength?

A

The force due to gravity per unit mass (kg)

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18
Q

What is your weight in freefall?

A

0 Newtons

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19
Q

What formula is used to work out the component of weight parallel to the slope?

A

F = mgsinØ

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20
Q

What is the resultant of a number of forces?

A

the single force that would have the same effect as all the other forces OR the vector sum of all the forces

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21
Q

What is the definition for Conservation of energy?

A

Energy cannot be created or destroyed, only converted from one form to another.

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22
Q

What is the definition of Conservation of momentum?

A

The total momentum before a collision is equal to the total momentum after a collision in the absence of external forces

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23
Q

What quantity is always conserved in a collision?

A

Momentum

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24
Q

How can an inelastic collision be identified?

A

Kinetic energy is lost - the total kinetic energy before the collision is greater than the total kinetic energy after the collision.

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25
Q

How can an elastic collision be identified?

A

The total kinetic energy before the collision IS equal to the total kinetic energy after the collision.

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26
Q

What is the definition of Impulse

A

Force on an object multiplied by the time the force acts for OR the change in momentum of an object.

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27
Q

Which two units can be used for momentum?

A

Ns OR kgms-1

28
Q

What can be calculated from the area under a Force - time graph?

A

Impulse OR Change in momentum

29
Q

A brick is dropped first onto concrete then onto a sponge surface. The same brick is dropped and it is dropped from the same height. On which surface does the brick exert the smallest force?

A

As the brick is dropped from the same height, it will start from rest in both cases and reach the same speed before it hits the surface. The change in momentum remains the same, mv-mu. The time of contact will increase on the spongy surface. Ft = mv-mu So the average force will decrease.

30
Q

What can be said about the Gravitational force?

A

It is always attractive.

31
Q

In the Gravitational Force equation what is the distance, r?

A

The distance, r, between the two objects is the distance between their centres of mass.

32
Q

What assumption is made when calculating the Gravitational force?

A

The objects are spherical

33
Q

What two principles underpin the theory of relativity?

A
  1. When two observers are moving at constant speeds relative to one another, they will observe the same laws of physics.
  2. The speed of light (in a vacuum) is the same for all observers.
34
Q

What is the definition for time dilation?

A

Time dilation is the difference in a time interval as measured by an object moving relative to a stationary observer.

35
Q

What is the definition for length contraction?

A

Length contraction is the difference in length (in the direction of motion) of an object moving relative to a stationary observer. Length contraction only takes place in the direction that the object is travelling.

36
Q

At what speeds would you have to take relativistic effects into account?

A

For small velocities i.e. less than 0.1 times the speed of light relativistic effects are negligibly small.

37
Q

When will time dilation become apparent?

A

The stationary observer and a person or object moving at relativistic speeds experience time passing in the same way. Only when they compare the times they have experienced do they notice a difference. The person who is stationary will have experienced a longer time in comparison.

38
Q

When will length contraction become apparent?

A

The stationary observer and a person or object moving at relativistic speeds experience length in the same way. Only when they compare the lengths they have experienced do they notice a difference. The person who is stationary will have experienced a shorter length in comparison.

39
Q

What does the Doppler effect apply to?

A

All waves

40
Q

What happens to the source frequency during the Doppler Effect?

A

Nothing - it remains constant

41
Q

For Doppler Effect calculations you use the following formula.

Describe when you should use the + and when you should use the - in the equation.

A

Sound source moving towards observer USE - as less time for waves to reach observer. Sound source moving away from observer USE + as more time for waves to reach observer.

42
Q

Explain what a stationary observer would notice if a car with a siren on it was moving towards them.

A

Each wave front is emitted closer to the observer than the previous wave. So each wave front reaches the observer in less time than the previous wave. This causes the number of wave fronts arriving at the observer per second to increase. So the frequency the observer experiences is increased.

43
Q

Explain what a stationary observer would notice if a car with a siren on it was moving away from them.

A

Each wave front is emitted further away from the observer than the previous wave. So each wave front reaches the observer in a longer time than the previous wave. This causes the number of wave fronts arriving at the observer per second to decrease. So the frequency the observer experiences is decreased.

44
Q

Explain Redshift

A

Explanation Light from distant galaxies and stars can be observed on Earth. These galaxies and stars are moving away from us. So each light wave front is emitted from slightly further away than the last. This causes the number of wave fronts arriving per second at the Earth to decrease. This is an apparent decrease in frequency, which results in an increase in the wavelength of the light we see on Earth. So the light is shifted to longer (more red) wavelengths. The frequency of the light emitted by the source does not change.

45
Q

What is the definition for redshift?

A

Redshift of light - Light from stars or galaxies moving away from us is shifted to longer wavelengths and so the redder wavelengths of the spectrum.

46
Q

What is Hubbles Law?

A

Hubble’s Law is the relationship between the recession velocity of a galaxy as it moves away from us and its distance.

47
Q

Give one application for Hubbles Law

A

Calculating the age of the universe

48
Q

Explain how Hubble’s Law can estimate the age of universe.

A

Hubble’s observations show galaxies move away from each other and Earth in all directions. So the universe must be expanding. So if you could go back in time the galaxies etc. would be closer together, so if you go back to the point when all the galaxies were at one point, this would be the beginning of the universe. t=1/H0

49
Q

What is the evidence for dark matter?

A

The mass of a galaxy can be estimated by the orbital speed of the stars within it. From our estimations there is not enough mass to keep the galaxy together. Therefore there must be mass we cannot detect. This is dark matter.

50
Q

What is the evidence for dark energy?

A

Distant objects are accelerating away from us. There must be something to overcome the gravitational forces acting. The extra energy that these objects gain is called dark energy.

51
Q

What is the definition for The Big Bang?

A

The Universe was initially in a hot and very dense state and then expanded rapidly. OR All the matter in the universe was in an unimaginably small volume, almost a point, and rapidly expanded.

52
Q

The colour of a star tells us about it’s surface temperature.This colour can be split into all the radiations being emitted producing a blackbody graph. What do the blackbody radiation graphs of stars tell us?

A

The temperature of stellar objects is related to the distribution of emitted radiation over a wide range of wavelengths. The hotter the object the shorter the peak wavelength emitted. A hotter star will emit more radiation per unit surface area per unit time than a cooler one. (If they are similar in mass, surface area etc)

53
Q

What evidence is there that Cosmic Microwave Background Radiation supports Big Bang Theory?

A

• It is the dominant source of radiation in the Universe • It is very uniform throughout the Universe. • It shows the characteristics of blackbody radiation. • It has a temperature of approx. 3K (2·74K) due to cooling on expansion of the universe. • CMBR is thought to be the “afterglow” of the Big Bang, cooled to a faint signal in the microwave region.

54
Q

What evidence is there to support Big Bang Theory?

A
  • Expanding Universe
  • Cosmic Microwave Background Radiation
  • Explanation Olber’s Paradox (Why we see a dark sky)
  • Abundance of Hydrogen and Helium in the Universe
55
Q

What is Olber’s Paradox?

A

Olber said that if the universe was infinitely old and static that we should see stars in all directions. But the universe is not infinitely old it had a beginning (so light from distant stars may not have had time to reach us yet) and the universe is expanding (galaxies are moving away from us so the light may be redshifted into the infra-red part of the spectrum so we will not see the light).

56
Q

Why is the abundance of helium and hydrogen in the universe evidece for the Big Bang?

A

Big Bang Theory says that matter started as a very simple form that became more complex as time passed. The simplest elements would have formed first and existed in larger quantities than heavier elements, which would not exist until stars are born. These first elements were hydrogen and helium. The fact that there is an abundance of these elements in the universe supports the theory.

57
Q

Why does Redshift support Big Bang Theory?

A

Redshift occurs because galaxies are moving away from us. This is the continued expansion from the Big Bang. If the galaxies were not moving away the light would not experience redshift.

58
Q

Explain what would happen to your apparent weight if you were standing on a set of Newton scales and were in a lift that was travelling at a constant speed.

A

Your apparent weight would = real weight as the forces are balanced.

59
Q

What would happen to your apparent weight if you were standing on a set of Newton scales and were in a lift that was accelerating upwards?

A

Your apparent weight would increase, It would be equal to your weight plus the force to cause the acceleration upwards.

60
Q

What would happen to your apparent weight if you were standing on a set of Newton scales and were in a lift that was de-accelerating upwards?

A

Your apparent weight would decrease, It would be equal to your weight minus the force to cause the de-acceleration upwards.

61
Q

What would happen to your apparent weight if you were standing on a set of Newton scales and were in a lift that was de-accelerating downwards?

A

Your apparent weight would increase, It would be equal to your weight plus the force to cause the de-acceleration downwards.

62
Q

What would happen to your apparent weight if you were standing on a set of Newton scales and were in a lift that was accelerating downwards?

A

Your apparent weight would decrease, It would be equal to your weight minus the force to cause the acceleration downwards.

63
Q

A ball is thrown upwards into the air and is allowed to fall and bounce. See graph.

Between which points on the graph is the ball travelling upwards?

A

A-B, E-F,

64
Q

A ball is thrown upwards into the air and is allowed to fall and bounce. See graph.

Between which points on the graph is the ball hitting the ground?

A

C-E, G-I

65
Q

A ball is thrown upwards into the air and is allowed to fall and bounce. See graph.

At which points is the ball at the top of it’s flight?

A

B, F

SA H Physics (4 decks)

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