6. Space research and 6. Space research and exploration of space increases exploration of space increases

our understanding of the our understanding of the Earth‘s own environment, the Earth‘s own environment, the

Solar System Solar System and the Universe.and the Universe.

4. Rapid advances in 4. Rapid advances in technologies over the technologies over the past fifty years have past fifty years have

allowed the exploration allowed the exploration of not only the Moon, but of not only the Moon, but the Solar System and, to the Solar System and, to an increasing extent, the an increasing extent, the

Universe. Space Universe. Space exploration is becoming exploration is becoming

more viable.more viable.

1. Scientists have 1. Scientists have drawn on drawn on

advances in areas advances in areas such as such as

aeronautics, aeronautics, materials science,materials science,

robotics, robotics, electronics, electronics,

medicine and medicine and energy energy

production to production to develop viable develop viable

spacecraft.spacecraft.

2. Perhaps the most 2. Perhaps the most dangerous parts of any dangerous parts of any space mission are the space mission are the launch, re-entry and launch, re-entry and landing. A huge force is landing. A huge force is required to propel the required to propel the rocket a sufficient rocket a sufficient distance from the Earth distance from the Earth so that it is able to so that it is able to either escape the either escape the Earth’s gravitational Earth’s gravitational pull or maintain an pull or maintain an orbit.orbit.

3. Following a 3. Following a successful mission, successful mission,

re-entry through the re-entry through the Earth’s atmosphere Earth’s atmosphere

provides further provides further challenges to challenges to scientists if scientists if

astronauts are to astronauts are to return to Earth return to Earth

safely.safely.

5. Information from 5. Information from research undertaken in research undertaken in

space programs has space programs has impacted on society impacted on society

through the development through the development of devices such as of devices such as

personal computers, personal computers, advanced medical advanced medical

equipment, equipment, communication satellites communication satellites

and the accurate and the accurate mapping of natural mapping of natural

resources.resources.

7. This module 7. This module increases students’ increases students’

understanding of the understanding of the history, nature and history, nature and practice of physics practice of physics

and the implications and the implications for the environment.for the environment.

Gather secondary

information to predict the value of acceleration

due to gravity on other planets

1. The Earth has agravitational field that

exerts a force onobjects both on it and

around it

What planets should I travel to if I want to lose some weight?

W

W

W

W

W

W

Question 1

Siobhan has a mass of 55 kg. She is in a rocket descending to the surface of Mars and is

standing on some scales. The scales are reading 94 N whilst she descends at a rate of

2 ms-2.

(a) Determine the resultant force acting on Siobhan.

(b) Determine the acceleration due to gravity on Mars.

Analyse information using the expression F=mg to determine the weight force for a body on

Earth and for the same body on other planets

(a) 1 markSiobhan is a mass of 55kg accelerating at 2 m/s2 downwardsF = maF = 55 x 2F = 110 N

(b) 1 markReaction force, R, is reduced, soR = mg – mamg = ma + Rg = (ma + R)/mg = (110 + 94)/55g = 3.7 ms-2

Question 1

A student wanted to determine the acceleration due to gravity using a simple pendulum.

Given the formula

42l g = ––––

T2

where g is the acceleration due to gravity

l is the length of the string connecting the bob to the fixed roof support

T is the period of the oscillation of the pendulum.

(a) Outline the experimental procedure you would use to determine the

acceleration due to gravity.

(b) Sketch the shape of the graph you would obtain, showing the relationship

between l & T and l & T2.

(c) What sources of error would there be in your experimental procedure?

Perform an investigation and gather information to determine a value for acceleration due to gravity using pendulum motion or computer assisted technology and identify reasons for possible variations from the value 9.8 m/s2

Experiment:

Computer simulation of pendulum

1 (a) 5 marks

The apparatus was set up as shown with a length of 1.0 m for the string connecting

the bob to the fixed position. The pendulum was drawn back and released. The time

taken for twenty oscillations was measured. This was repeated four times and the

average period was determined. The whole experiment was repeated for lengths of

string, 1.2 m, 1.4 m, 1.6 m, 1.8m , 2.0 m. A graph of 42l and T2 was obtained with

the line of best fit drawn and the gradient determined. The gradient is the acceleration

due to gravity.

(b) 2 marks

(c) 2 marks

Possible sources of error would include limitations of the scale of the measuring

devices, air resistance on the bob, friction where the string attached to the fixed top.

PLUS human errors in timing…

Identify reasons for possible variations from the value 9.8 m/s2

Identify reasons for possible variations from the value 9.8 m/s2

The value of acceleration due to gravity at the surface of the Earth varies from the usually accepted value of 9.8 m s-2, due to a number of factors:

•The Earth’s lithosphere varies in structure, thickness and density. Thickness variations are a product of the source and history of the material. Oceanic crust is thinner than continental crust. Continental crust is thickest under mountain ranges. Density variations occur due to the presence of concentrated and large mineral deposits or petroleum gas and related liquids trapped in sedimentary rocks and structures. All of these variations can influence local values of g.

(NSW HSC on-line …continued over…)

Identify reasons for possible variations from the value 9.8 m/s2

•The Earth’s globe is flattened at the poles. This means that the distance of the surface from the centre of the Earth is less at the poles, which increases the local value of g.

•The spinning Earth also affects the value of g. At the equator, the spin effect is greatest resulting in a lowering of the value of g. As you travel from the equator to the poles, the spin effect on g shrinks to zero.

•As a result of the above, the value of g at the surface of the Earth varies between 9.782 m s-2 at the equator and 9.832 m s-2 at the poles

•The value of g reduces with altitude above the surface of a planet, becoming zero only at an infinite distance. At low Earth orbit altitude, the value of g is approximately 8.9 ms-2.

(NSW HSC on-line)

Using Newton’s Law of Universal Gravitation, you need the mass

and radius of the planet.

1. The Earth has agravitational field that

exerts a force onobjects both on it and

around it

Define weight.What information do I need to predict the acceleration due to gravity on other planets?

Identify reasons for possible variations from the value 9.8 m/s2.

The value of acceleration due to gravity at the surface of the Earth varies from the usually accepted value of 9.8 m s-2, due to a number of factors:

•The Earth’s lithosphere varies in structure, thickness and density. Thickness variations are a product of the source and history of the material. Oceanic crust is thinner than continental crust. Continental crust is thickest under mountain ranges. Density variations occur due to the presence of concentrated and large mineral deposits or petroleum gas and related liquids trapped in sedimentary rocks and structures. All of these variations can influence local values of g.

•The Earth’s globe is flattened at the poles. This means that the distance of the surface from the centre of the Earth is less at the poles, which increases the local value of g.

•The spinning Earth also affects the value of g. At the equator, the spin effect is greatest resulting in a lowering of the value of g. As you travel from the equator to the poles, the spin effect on g shrinks to zero.

•As a result of the above, the value of g at the surface of the Earth varies between 9.782 m s-2 at the equator and 9.832 m s-2 at the poles

•The value of g reduces with altitude above the surface of a planet, becoming zero only at an infinite distance. At low Earth orbit altitude, the value of g is approximately 8.9 ms-2.

(NSW HSC on-line)

Potential Energy increases as distance increases, and

Ep at infinity = 0, hence the negative sign.

So if r decreases,

P.E. decreases (becomes more negative).

Define gravitational potentialenergy as the work done tomove an object from a very

large distance away to a pointin a gravitational field

Ep = -Gm1m2/r

Where

r = distance between centres of mass

To calculate the energy required to move a mass in a gravitational field or change in energy, calculate Ep for

both points and work out the difference

r

m1 m2

Define gravitational potential energy.

How do I calculate the ‘energy required to move a mass in a gravitational field’ or ‘change in energy’?

Where

r = distance between centres of mass

Calculate Ep for both points and work out the difference

r

m1 m2

Gravitational potentialenergy is the work done to move an

object from a very large distance away to a point in a gravitational

field

Ep = -Gm1m2/r.

A satellite of mass 200 kg is to be fired so that it

achieves an orbit at 300 km around the Earth

(the Earth has a radius of 6 378 km, m=6x1024 kg, G = 6.67x 10-11)

(a) Determine the energy required to raise the

satellite (not the rocket or fuel) to the required altitude.

(a) 1 mark

E = -Gm1m2/(r+h) – (-Gm1m2/r)

E =(-6.67x 10-11 x 200 x 6 x 1024/(6.378x106 + 3x105)) - (-6.67x 10-11 x 200 x 6 x 1024/6.378x106)

E = 5.64 x 108 J