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P2.2.1 Forces and Energy P2 Physics Mr D Powell 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 Consolidation • 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 • 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 Mr Powell 2012 Index 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) W=Fxd P = E/t d) Work done against frictional forces. e) Power is the work done or energy transferred in a given time. P = E/t Mr Powell 2012 Index Formulae help... W=Fxd P = E/t Ep = mgh Ek = ½ mv2 Mr Powell 2012 Index When I move these objects I do what... Mr Powell 2012 Index a/b) What is work done? C/D TASK: 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) Mr Powell 2012 1. 2J 2. 15J 3. 1200J Index a/b) More on W.D. TASK: Explaining / Devising B/C 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 Mr Powell 2012 Index Friction at work TASK: Explain several examples where friction effects your life. C Mr Powell 2012 Index Plenary... 1. 2. 3. 4. 96J 96J 90 & 4500J WD= mgh or WD/mg= h = 270J/450N = 0.6m Mr Powell 2012 Index 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 Mr Powell 2012 Index Multichoice Mr Powell 2012 Index 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 Mr Powell 2012 Index P2.2.1 Forces and Energy Ep = mgh 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 Ek = ½ mv2 Mr Powell 2012 Index What is happening... What happens here.... Where has the energy gone? Mr Powell 2012 Index Pendulum... PE max KE 0 PE max KE 0 PE 0 KE max 1 2 KE m v 2 PE m gh KE PE 1. Label the diagram with the energy changes... Mr Powell 2012 Index Where does it come from? Mr Powell 2012 Index Interactive Mr Powell 2012 Index Kinetic Energy of a horse.. A horse (with 3 legs) of mass 175kg walks at a velocity of 3ms-1 its kinetic energy is found as; 1 2 KE m v 2 1 1 2 KE 175kg 3m s 2 1 KE 175kg 9m 2 s 2 2 KE 87.5kg 9m 2 s 2 KE 787.5kgm2 s 2 1 2 KE m v KE 787 . 5 J 2 1 Quick Version..... KE 175 32 2 KE 787.5 J Mr Powell 2012 Index Another worked example? Mr Powell 2012 Index Sorting.... A/B 2250 kgm2s-2 or 2250J 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? 1000 kgm2s-2 or 1000J 187.5 kgm2s-2 or 187.5J 100 kgm2s-2 or 100J NB: take care with your units for KE 2000 kgm2s-2 or 2000J Mr Powell 2012 Index Practical Examination of Kinetic Energy The 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? Mr Powell 2012 Index Practical Examination of Kinetic Energy (HT) Here 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 ∆h (m) 0.05 0.1 0.16 0.20 PE of ball (J) 0.25 0.72 0.80 1.00 ∆t to travel 1m from x -> y 0.98 0.71 0.57 0.50 Velocity ms-1 1.02 1.75 2.00 A/B 1.41 TASK: Complete the table by doing 4 calculations. There two ways of thinking about it! Mr Powell 2012 Index Multichoice PE = mgh KE = ½mv2 Mr Powell 2012 w = mg Index Homework Questions... 1. 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? TASK: You have these 6 questions on a worksheet to fill in and then check next lesson. 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? orking 4. If the mass of the plane doubles by what factor does the kinetic energy increase for the same speed? nswer 5. If the velocity of the plane increases by a factor of x3 by what factor does the kinetic energy increase. nit 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? Mr Powell 2012 Index Answers.... 1 2 KE m v 2 1) See right....... 2 1 KE 195kg 666m s1 2 2) twice the speed of sound; mach 2 1 2 2 KE 195 kg 443556 m s 3) F=ma, reduce the mass. Since the 2 acceleration will be increased therefore KE 97.5kg 443556m 2 s 2 the force is reduced to accelerate the plane. Same argument also applies to streamlining 4) x2 KE 43246710kgm2 s 2 KE 43246710J KE 43.2 MJ 5) x9 or 32 orking 6) 1050J x 0.7 or (1050J x 70%) /100% gives; 735J. The 30% of wasted energy is lost in heat to the surroundings. nswer nit Mr Powell 2012 Index W.D. In context 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 A-B Mr Powell 2012 Index Formulae Warm Up...... You have 2 minutes to rearrange and sort out these formulae 2 1) 2) Simplify? Make the square the subject? 2 3) Find the triangle? Mr Powell 2012 Index Formulae...... You have 2 minutes to rearrange and sort out this formulae 1 2 KE mv 2 to get make the following the subject... v= m= be prepared to come up to the board and demonstrate how you got there! Mr Powell 2012 Index Back to waterfalls... We can also do something clever when thinking of this formula when looking at Kinetic Energy as well. EGPE = mgh EKE = 0.5mv2 (eq1) (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 1 2 m gh m v 2 2m gh m v2 2 gh v 2 2 gh v 20h v Mr Powell 2012 Index What is the speed of the water... 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 10.00 1 2 m gh m v 2 2m gh m v2 10 14.14 2 gh v 2 20 20.00 2 gh v 100 44.7 20h v Mr Powell 2012 Index 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) Mr Powell 2012 Index Plenary Questions 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 Task: Do these questions / activities on your own without help from anyone! 1 2 KE mv 2 WD Fd Mr Powell 2012 Index Extension Quick Questions PE = mgh KE = ½mv2 w = mg KE = ½mv2 = 0.5 x 80 x 102 = 4000J KE = ½mv2 = 0.5 x 500 x 302 = 225kJ KE = ½mv2 = 0.5 x 10,000 x 2002 = 9MJ 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 Mr Powell 2012 Index Multichoice... Mr Powell 2012 Index P2.2.1 Forces and Energy P2.2.1 Forces and Energy P2.2.1 Forces and Energy a) When a force causes an object to move through a distance work is done. a) When a force causes an object to move through a distance work is done. 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 xd b) Work done, force and distance, are related by the equation: W = F xd b) Work done, force and distance, are related by the equation: W = F xd 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) 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) 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. d) Work done against frictional forces. d) Work done against frictional forces. e) Power is the work done or energy transferred in a given time. P = E/t e) Power is the work done or energy transferred in a given time. P = E/t 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 f) Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational field. Ep = mgh f) Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational field. Ep = mgh a) The kinetic energy of an object depends on its mass and its speed. a) The kinetic energy of an object depends on its mass and its speed. a) The kinetic energy of an object depends on its mass and its speed. Ek = ½ mv2 Ek = ½ mv2 Ek = ½ mv2 Formulae help... W=Fxd P = E/t Ep = mgh Ek = ½ mv2 Formulae help... W=Fxd P = E/t Ep = mgh Ek = ½ mv2 Work Done Revision Work Done Revision KE & PE Revision KE & PE Revision