2. Gravitational fields And Orbits

Question 1

Difference between EF and GF

Answer 1

Charge moves from positive to negative
GF the mass is only a positive value

Question 2

Similarities between EF and GF

Answer 2

The relationship between their fieldstrengths and distance is an inverse square relationship
Fieldstrength becomes 0 at infinite away from a point

Question 3

Gravitational force is proportional to …

Answer 3

mass

Question 4

Weight =

Answer 4

mass x gravitational field strength

Question 5

Gravitational field strength

Answer 5

force / mass

Question 5

How could you show the earths gravitational field strength close to earth?

Answer 5

Using a pendulum with the same mass, use time and mass to calculate g in a period

Question 6

Force between two masses equation

Answer 6

F = GM1M2 / r^2

Question 6

What is the G constant

Answer 6

6.67 x 10^-11

Question 6

what does r represent in the force mass equation

Answer 6

the distance between the centres of the two masses

Question 7

Gravitational potential

Answer 7

the work done in bringing unit mass from infinity to that point

Question 7

grativitational potential equation

Answer 7

Vg = -GM / r

Question 8

gravitational energy equation

Answer 8

energy = m x g x change in h

Question 9

work done equation

Answer 9

w = egrav= m x change in potential energy

Question 10

on a graph how can you find the potential difference`

Answer 10

the area under the g -r graph

Question 11

What other laws can be used to explain keplers laws

Answer 11

Newtons laws of gravtitation

Question 12

What are keplers three laws

Answer 12

1. The orbit is an elliptical shape with the sun at one focus
2. A line joining the planet and the sun sweeps around in equal intervals of time and area
3. The square of time period is proportional to the cube distance from the sun

Question 13

What is the equation linking centripetal motion and orbits

Answer 13

GMm/r² = mv²/r

Question 14

What is the doppler effect

Answer 14

If the object is moving towards the observer then the frequency appears to increase so is blueshifted.

If the object is moving away then the frequency decreases so is redshifted

Question 15

Doppler effect equation

Answer 15

Changing in wavelength / wavelength = velocity of object / speed of light

Question 16

The difference between observed wavelength and wavelength

Answer 16

Observed is the bottom of the equation which is the one seen from the galaxy
Wavelength is the normal length found in the lab on earth
So change in wavelength is the difference between the two values

Question 17

Equation for time period of an orbit

Answer 17

T = 2Pi x square root of d³/ G ( m1 + m2)

Question 18

What is the relationship between m1 and m2

Answer 18

The value of m1 is astronomically bigger than m2 so if need be we can assume that the mass of m2 is insignificant to the equation
This is the same as keplers third law

Question 19

Radius of planet equation

Answer 19

r1 = (m2 / m1 + m2) x d

Question 20

What is hubbles law

Answer 20

V = H⁰ x d
The recessional velocity is equal to hubbles constant time distance between earth and the galaxy
It also explains the relationship that the speed of travel is proportional to the distance travelled

Eg. The further they are the faster they are moving

Question 21

What is hubbles constant

Answer 21

2.3 x 10 ^-18 s^-1

Question 22

How do you estimate the age of the universe

Answer 22

Use 1 / hubbles constant which equals time in seconds V = d/t so can substitute into equation

Question 23

Why would the calculated age of the universe be different to the actual age

Answer 23

The calculated value assumes a constant rate of expansion using hubbles constant which we know isn't true

Question 24

Equation for the critical density of the universe

Answer 24

Pc = (3H⁰)² / 8Pi x G

Question 25

What is dark matter

Answer 25

A type of matter that cannot be observed using EM radiation however we know it exists

Question 26

How do we know dark matter exists?

Answer 26

1. Use a velocity distance graph to show the difference between observed and calculated values for a galaxy 2. Show that v is proportional to 1 / Square root of radius ( should work for all sections of the galaxy) 3. Explain that the difference on the graph shows there must be other mass present 4. As this mass is not seen it is written as dark matter 5. If we didn't have dark matter then the galaxies wouldn't be able to rotate at the speeds it does

Question 27

What is it meant by the critical density of the universe

Answer 27

The average density of the universe needed to halt its expansion

Question 28

How do you explain keplers third law with equations

Answer 28

Force on two objects (orbits) = Centripetal force Rearrange to get time squared is proportional to radius cubed

Question 29

What is baryonic mass

Answer 29

The mass made from baryons like protons and neutrons

Question 30

What is the higgs boson

Answer 30

An elementary particle observed by scientists to suggest the presence of dark matter