P2.2.1 Forces and EnergyP2 Physics

KS4 ADDITIONAL SCIENCEMr D Powell

Mr Powell 2012Index

Connection

• Connect your learning to the content of the lesson

• Share the process by which the learning will actually take place

• Explore the outcomes of the learning, emphasising why this will be beneficial for the learner

Demonstration

• Use formative feedback – Assessment for Learning

• Vary the groupings within the classroom for the purpose of learning – individual; pair; group/team; friendship; teacher selected; single sex; mixed sex

• Offer different ways for the students to demonstrate their understanding

• Allow the students to “show off” their learning

Activation

• Construct problem-solving challenges for the students

• Use a multi-sensory approach – VAK• Promote a language of learning to

enable the students to talk about their progress or obstacles to it

• Learning as an active process, so the students aren’t passive receptors

Consolidation

• Structure active reflection on the lesson content and the process of learning

• Seek transfer between “subjects”• Review the learning from this lesson and

preview the learning for the next• Promote ways in which the students will

remember• A “news broadcast” approach to learning

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P2.2.1 Forces and Energy

a) When a force causes an object to move through a distance work is done.

b) Work done, force and distance, are related by the equation: W = F x d

c) Energy is transferred when work is done. (Candidates should be able to discuss the transfer of KE i.e... shuttle re-entry or meteorites burning up in the)

d) Work done against frictional forces.

e) Power is the work done or energy transferred in a given time. P = E/t

W = F x d

P = E/t

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Formulae help...

W = F x d

P = E/t

Ep = mgh

Ek = ½ mv2

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When I move these objects I do what... S

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a/b) What is work done? AC/DTASK: Summarise this idea

then answer the questions

1. When I move an apple (1N weight) a distance of 2m along a desk what is the work done?

2. When I move 0.5kg a distance of 3m along a desk what is the work done?

3. When a weight lifter lifts a weight of 80kg a height of 1.5m what is the work done? (mgh)

1. 2J2. 15J3. 1200J

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a/b) More on W.D. D

1. Using the formulae for reference can you explain what happens to the W.D. If you have a bigger mass or larger distance to move your object?

2. Can you think of a formulae which could relate Power to Work Done. Write it out and explain how it works....

3. Write out your own example of a “worked problem” for another situation

B/C

TASK: Explaining / Devising

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Friction at work

C

TASK: Explain several examples where friction effects your life. D

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Plenary... D

1. 96J2. 96J3. 90 & 4500J 4. WD= mgh or WD/mg= h = 270J/450N = 0.6m

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Power

This is a very easy thing to look at when we consider work done.

Before we have looked at how energy is transferred via work done (see example below).

If you want to think about the power you simply divide the energy transferred by how long it to transfer...

P = E/t

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Multichoice D

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Summary Questions II

WD = Fd = 20N x 1.5m = 30Nm = 30J

WD = Fd = 600N x 100m = 60,000Nm = 60,000J = 60kJ

WD = Fd = 3000N x 30m = 90,000Nm = 90,000J = 90kJ

E = Pt so E / t = P = 60,000J / 20s = 3000J/s = 3000W

E = Pt so E / t = P = 90,000J / 20s = 4500J/s = 4500W

D

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P2.2.1 Forces and Energy

e) Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational field.

Ep = mgh

f) The kinetic energy of an object depends on its mass and its speed.

Ek = ½ mv2

Ep = mgh

Ek = ½ mv2

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What is happening... S

Where has the energy gone?

What happens here....

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Pendulum...

PEKE

hmgPE

mvKE

2

2

1

0

max

KE

PE

0

max

KE

PE

max

0

KE

PE 1. Label the diagram with the energy changes...

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Where does it come from?

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Interactive

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Kinetic Energy of a horse..

JKE

skgmKE

smkgKE

smkgKE

mskgKE

mvKE

5.787

5.787

95.87

91752

1

31752

12

1

22

22

22

21

2

A horse (with 3 legs) of mass 175kg walks at a velocity of 3ms-1 its kinetic energy is found as;

JKE

KE

mvKE

5.787

31752

12

1

2

2

Quick Version.....

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Another worked example?

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TASK: Firstly work in a pair and guess sort these vehicles then work out the missing KE values and then sort them into which has the largest and which has the smallest?

Sorting....A/B

NB: take care with your units for KE

2250 kgm2s-2 or 2250J

187.5 kgm2s-2 or 187.5J

1000 kgm2s-2 or 1000J

2000 kgm2s-2 or 2000J

100 kgm2s-2 or 100J

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Practical Examination of Kinetic Energy DThe kinetic energy of an object is the energy it has due to its motion. It depends on its mass and its speed We can investigate how the kinetic energy of a ball depends on its speed.

The ball is released on a slope from a measured height above the foot of the slope. We can calculate the gravitational potential energy it loses from its weight and its drop of height. The kinetic energy it gains is equal to its loss of gravitational potential energy.

The ball is timed, using light gates, over a measured distance between X and Y after the slope.

Q) How do light gates improve the quality of the data you can collect in this investigation?

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∆h (m) 0.05 0.1 0.16 0.20PE of ball (J) 0.25 0.72 1.00∆t to travel 1m from x -> y 0.98 0.57 0.50Velocity ms-1 1.02 2.00

Practical Examination of Kinetic Energy (HT) DHere are some results for a 0.5kg ball which has been dropped.

Can you work out the missing values if the formulas are;

EGPE = mgh

EKE = ½mv2

d/t = v

1.41 1.75

0.71

0.80

TASK: Complete the table by doing 4 calculations. There two ways of thinking about it!A/B

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Multichoice PE = mgh KE = ½mv2 w = mg

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Homework Questions... H1. Work out the kinetic energy of a fighter aircraft with

a mass of 195kg travelling at a speed of 666ms-1.

2. What is the significance of the speed of the fighter aircraft?

3. The designers of the Euro fighter Jet want to improve the acceleration of the plane. How can they achieve this without using larger engines? Justify you answer?

4. If the mass of the plane doubles by what factor does the kinetic energy increase for the same speed?

5. If the velocity of the plane increases by a factor of x3 by what factor does the kinetic energy increase.

6. A passenger plane burns up 70kg of fuel which contains 1050J of energy to get to a height of 700m. Taking account that the plane is 70% efficient, how much potential energy does the plane now have at this height?

TASK: You have these 6 questions on a worksheet to fill in and then check next lesson.

Working

Answer

Unit

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Answers.... H1) See right.......

2) twice the speed of sound; mach 2 3) F=ma, reduce the mass. Since the acceleration will be increased therefore the force is reduced to accelerate the plane. Same argument also applies to streamlining 4) x2 5) x9 or 32

6) 1050J x 0.7 or (1050J x 70%) /100% gives; 735J. The 30% of wasted energy is lost in heat to the surroundings.

MJKE

JKE

skgmKE

smkgKE

smkgKE

mskgKE

mvKE

2.43

43246710

43246710

4435565.97

4435561952

1

6661952

12

1

22

22

22

21

2

Working

Answer

Unit

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W.D. In context

A-B

TASK:

1. Logically reason out what is happening in the diagram.

2. Draw out your own copy and label what is going on.

3. Compare what is happening here to the formulae you have already covered. (Hint: W = mg)

Ep = mgh

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Formulae Warm Up......

You have 2 minutes to rearrange and sort out these formulae

2

Find the triangle?3)

Make the square the subject?2)

Simplify?2

1)

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Formulae......

You have 2 minutes to rearrange and sort out this formulae

to get make the following the subject...

v = m =

be prepared to come up to the board and demonstrate how you got there!

2

2

1mvKE

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Back to waterfalls...

We can also do something clever when thinking of this formula when looking at Kinetic Energy as well.

EGPE = mgh (eq1)

EKE = 0.5mv2 (eq2)

If I think of a transfer involving the energy at the top of a waterfall (GPE) and energy at the bottom (mainly KE)

I can work out the speed of the water falling by equating the two equations and assuming all the energy is transferred to kinetic.

In every case we find a value of “g” gravity as 10 m/s2

vh

vhg

vhg

mvhmg

mvhmg

20

2

2

2

2

1

2

2

2

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What is the speed of the water...

vh

vhg

vhg

mvhmg

mvhmg

20

2

2

2

2

1

2

2

2

Using this idea can you apply the formula and fill in the grid for water which drops from different heights.

You will need to use the Sqrt button on your calculator...

h (m) V (in m/s)

5

10

20

100

h (m) V (in m/s)

5 10.00

10 14.14

20 20.00

100 44.7

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Physics of Space Battles - Advanced

We think of the EM spectrum from Year 10 as having more energy as (wavelength) is shorter. (think UV -> Gamma)

The actual reason for this is because the energy for each photon of light is found from E=hf. (h is a constant, f = frequency )

But what about simply using a matter thrower.

Energy of particles is found from 0.5mv2

Just throw rocks fast enough and they have lots of energy!

Task: Now you have watch the movie make a comment in your own words (you can use my help) to explain what you have seen. What do you think? (1 paragraph)

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Plenary Questions Task: Do these questions / activities on your own without help from anyone!1. Copy down the equation for Kinetic

Energy in your book.

2. Use the formulae to explain why an object with more mass would have more KE. (explain in detail)

3. Use the formulae to explain why an object with double the velocity would have four times the KE. (explain in detail

4. What is the main point of the movie you saw in relation to “space physics”

5. Calculate the kinetic energy of a ball of mass 0.5kg thrown at a speed of 5ms-1

2

2

1mvKE

FdWD

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Extension Quick Questions PE = mgh KE = ½mv2 w = mg

KE = ½mv2 = 0.5 x 80 x 102 = 4000J

PE = mgh = 10m x 10 N/kg x 100kg = 10,000 Nm = 10,000J = 10KJ

PE = mgh = 3000m x 10 N/kg x 60kg = 1,800,000 Nm = 1.8MJ

PE = mgh = 50m x 10 N/kg x 0.100kg = 50 Nm = 50J

KE = ½mv2 = 0.5 x 500 x 302 = 225kJ

KE = ½mv2 = 0.5 x 10,000 x 2002 = 9MJ

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Multichoice...

P2.2.1 Forces and Energy

a) When a force causes an object to move through a distance work is done.

b) Work done, force and distance, are related by the equation: W = F x d

c) Energy is transferred when work is done. (Candidates should be able to discuss the transfer of KE i.e... shuttle re-entry or meteorites burning up in the)

d) Work done against frictional forces.

e) Power is the work done or energy transferred in a given time. P = E/t

f) Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational field.

Ep = mgh

g) The kinetic energy of an object depends on its mass and its speed.

Ek = ½ mv2

P2.2.1 Forces and Energy

a) When a force causes an object to move through a distance work is done.

b) Work done, force and distance, are related by the equation: W = F x d

c) Energy is transferred when work is done. (Candidates should be able to discuss the transfer of KE i.e... shuttle re-entry or meteorites burning up in the)

d) Work done against frictional forces.

e) Power is the work done or energy transferred in a given time. P = E/t

f) Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational field.

Ep = mgh

g) The kinetic energy of an object depends on its mass and its speed.

Ek = ½ mv2

P2.2.1 Forces and Energy

a) When a force causes an object to move through a distance work is done.

b) Work done, force and distance, are related by the equation: W = F x d

c) Energy is transferred when work is done. (Candidates should be able to discuss the transfer of KE i.e... shuttle re-entry or meteorites burning up in the)

d) Work done against frictional forces.

e) Power is the work done or energy transferred in a given time. P = E/t

f) Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational field.

Ep = mgh

g) The kinetic energy of an object depends on its mass and its speed.

Ek = ½ mv2

Formulae help...

W = F x d

P = E/t

Ep = mgh

Ek = ½ mv2

Formulae help...

W = F x d

P = E/t

Ep = mgh

Ek = ½ mv2

Work Done Revision Work Done Revision

KE & PE Revision KE & PE Revision