P2 Topic 10

Learning Objectives

• For an object to move in a circular path a force must act on it.• Energy can be converted from one form into another

but it cannot be made or destroyed.• New scientific theories are

not always derived through experimental methods.Learning outcomes:

• demonstrate understanding of and apply the principle of conservation of energy to examples involving gravitational potential energy, kinetic energy and other forms of

energy P2 10.7• describe a roller coaster or other ride, in terms of speed, acceleration, force and energy

P2 10.8• explain that an object moving in a circle at constant speed is accelerating P2

10.9• explain the resultant force acting on an object which is moving causes this

accelerationP2 10.10• recall that this force is directed to the centre of the circle P2 10.11

Assessment objectives:• show understanding of how scientific evidence is

collected and its relationship with scientific explanations and theories

• show understanding of how scientific knowledge and ideas change over time and how these changes are validated.

• apply concepts, develop arguments or draw conclusions related to familiar and unfamiliar situations

• analyse and interpret qualitative and quantitative data from different sources

• consider the validity and reliability of data in presenting and justifying conclusions.

Learning Outcomes• demonstrate understanding of and apply the principle of conservation of

energy to examples involving gravitational potential energy, kinetic energy and other forms of energy P2 10.7

• describe a roller coaster or other ride, in terms of speed, acceleration, force and energy P2 10.8

• explain that an object moving in a circle at constant speed is accelerating P2 10.9

• explain the resultant force acting on an object which is moving causes this accelerationP2 10.10

• recall that this force is directed to the centre of the circle P2 10.11• recognise that some theories, such as Einstein's theory of relativity, require creative imagination such as thought experiments, and do not emerge from

experimental data automaticallyP2 10.12• discuss the fact that some scientists are often reluctant to accept new

theories, such as Einstein’s relativity, when they overturn long-established explanationsP2 10.13

• explain that Einstein's theory of relativity is believed because it led to predictions which were tested successfully in different situations, such

as atomic clocks and cosmic rays.P2 10.14

keywords

• Relativity • Kinetic energy• Gravitational potential energy• Energy transfer• Acceleration

• Accuracy• Estimation • Reliability

What happens to the work done?

Power and energy; current = ,power = ,time = ,g = , first drop height = ,

second drop height = loop height =

Power and energy; current = ,power = ,time = ,g = , first drop height = , loop height =

Escape from this slide to move the captions to the right place on the diagram.

2 In this picture the arrow shows the direction of the resultant force.

Does the child keep moving in a circle or not? Explain your answer.

• P2.10 7a Testing the theory of relativity

Sort these statements into two groups:√ valid scientific reasons x non-scientific reasons for accepting or rejecting for accepting or rejecting

a new theory. a new theory.

You’ll need to ‘escape’ to move the words!

Einstein – genius or eccentric?The rumours were that:

He failed at school.

His relationships were odd.

He worked in the patent office in Berne, Switzerland because no one else would give him a job.

However in truth:

He did a lot of thought -‘gedanken’- experiments.

Outside, the establishment he could do his own thinking.....

1905

• This was a momentous year in the life of Einstein who wrote 5 tremendous papers – of which we remember 1,2 or 3.

• He wrote about special relativity.

• He wrote about brownian motion.

• He wrote about the relationship between energy and mass.

• What would the world be like if I were riding on a beam of light?

• What if my twin were just sitting at home?

If weight is a force, and the force can be:

Mass x gravitational field strength

Or mass x acceleration

• Why is ‘’’gravity’’’ just like an acceleration?

• Why is it the same for everything in one place?

Einstein – the thinker!?

If weight is a force, and the force can be:

Mass x gravitational field strength

Or mass x acceleration

• Why is ‘’’gravity’’’ just like an acceleration?

• Why is it the same for everything in one place?

All objects travel in straight lines at the same velocity unless a force acts on them…..

1. Objects travel in straight lines at constant velocity unless a force acts on them.

2. Planets move in orbit around stars. Stars move in orbits within galaxies. The force is gravitational and acts on the mass.

3. Energy is equivalent to mass and vice versa.

4. Light is energy so ..

5. Light is equivalent to a mass ..

6. So light beams bend past stars ..

7. because masses change direction past stars ..

8. So space is warped…..

Theory – predicts ....

• Einstein’s theory of relativity predicted that light could be affected by gravity, if the gravitational force was large enough. The gravity of a massive object such as a star would cause any light passing close by to bend slightly round the star.

• Einstein’s theory of general relativity changed the view of the world fundamentally.

a Why is it important to test the predictions made by a theory?

b How can testing the predictions of a theory help people to accept the theory?

• Einstein’s theory of relativity predicted that light could be affected by gravity, if the gravitational force was large enough. Yet on Earth, established scientific measurements showed light travelled in straight lines and that Newton’s laws told us about gravitational forces.

• Einstein’s theory of general relativity changed the view of the world fundamentally. For example, it proposed that mass could be changed into energy and vice versa. This led to huge changes in the theories of physics. But these changes were not accepted immediately. Many of the predictions could not be tested until the second half of the 20th century, when more accurate measurements became possible.

a Why is it important to test the predictions made by a theory?b How can testing the predictions of a theory help people to accept the

theory?