2. Atlas Ball Farmer’s walk Who is doing more work? When you do anything like running, jumping, writing and even sleeping we know you need energy to do them. However are you doing anything useful?

3. Work Done and Energy Transfer Consider holding the flaming torch like the Statue of Liberty. It would require you to consume food just to remain standing i.e. an input of energy, however we could replace the person by an inanimate object like a huge concrete statue which requires no energy input. Therefore is any work being done by the statue? The answer is obvious as no energy is being put in and the torch isn’t moving how can any work be done!!

4. In order to understand work we must first understand energy. Energy is the ability to do work Joules (J) Energy is the ability to do work measured in Joules (J) If you do work on an object such as lifting a bag, you lose energy and the bag gains potential energy. Energy cannot be created or destroyed as you know. systemssystem is an object or group of objects that we are considering the Physics of In Physics we sometimes talk about systems. A system is an object or group of objects that we are considering the Physics of. If a system does work, its energy decreases. When work is done on the system its energy increases.

5. Whenever a force causes an object to move, work is said to be done. It is the product of the magnitude of the force and the distance moved in the direction of the force. Whenever energy is transformed from one form to another work is said to be done! 1 Joule of work is done on an object when a force of 1 N cause it to move a distance of 1 m in the direction of the force This explains why the Statue of Liberty and you would effectively be doing no work holding up the torch. There is no resultant force and no movement!

6. In order to calculate the work done you use the following equation. Work Done = Force * Distance moved in direction of force Joules = N * m Joules = N * m (DO NOT CONFUSE WITH MOMENTS)  W = F  d When a system does work the amount of work it does is equal to the amount of energy gained by the second system. Hence Work done = Energy Transferred

7. How much work must be done to lift a 5kg bag 1.2m and place it on a table?

8. If the work being done within a system is not caused by a uniform force it is not possible to calculate the work done using the equation given. Instead we need to rely on graphical methods. Work done = The area under a Force – Displacement graph Force/N Displacement / m Work Done

9. Calculate the work done on the spring when it is compressed by 4.0cm. Work done =...................(3) The frog has a mass of 24 g and rises 0.60 m vertically into the air. Calculate the gravitational potential energy gained by the frog. Energy =...................(2) Compare your two answers for energy and explain how they are consistent with the law of conservation of energy. (2) (Total 7 marks) Force/N Compression/m 0 0 22 0.04 A toy frog has a spring which causes it to jump into the air. The force-compression graph for the spring is shown below.

10. Calculation of work done: Work = area under graph/average force × distance (1) = 1/2 × 0.040 m × 22 N (1) =0.44 J (1)3 [Allow any correct unit, e.g. N m. Penalise unit once only] [Fd ® + 0. 88 J gets 1/3] Calculation of energy: GPE = 0.024 kg × 9.81 (or 10) m s–2 × 0.60 m (1) = 0.14 J (1)2 Comparison: Some energy transferred to some other form (1) Reason [a mechanism or an alternative destination for the energy], e.g. (1)Friction, Air resistance, Heat transfer to named place [air, frog, surroundings etc], Internal energy, Vibrational energy of spring Sound OR quantitative comparison (0.3 J converted) [No e.c.f. if gpe > work]2 [7]

14. How much work must be done to drag a bag of rubbish 10m across a field by pulling on a string at 40° to the horizontal with a force of 250N?

15. Principle of Conservation of Energy States that …… Energy cannot be created or destroyed, merely changed from one form to another

16. Whenever a “machine” does it’s job it changes one form of energy to another. However this change is never perfect. In the case of light bulbs a lot of the energy is given off as heat. There are many types of energy changes we could investigate, one of which is the change of Gravitational Potential Energy into Kinetic. Many scenarios involve changes of energy but sometimes they are not so obvious. Where does the chemical energy needed for this lovely man to throw his darts go??

17. Ultimately all energy will change into heat due to friction but in between it may go through several stages which you should be able to identify. A boy sliding down a grassy bank – his speed is constant but where is the energy he is gaining from the Gravitational Potential Energy going ? If his speed is constant the Kinetic Energy is staying the same so what is happening? A car pulling a trailer with a constant force of 1000N should be accelerating but if it is travelling at a constant speed what is going on? If the force has been acting on the trailer for a longer distance then more Work has been done or more energy supplied to the trailer.

18. individual atom’s random kinetic energy Heat energy is more correctly called Thermal Energy but even more correctly called Internal energy which is linked to the individual atom’s random kinetic energy. electromagnetic forces potential energy Since there are electromagnetic forces between the atoms, they create stores of potential energy, like stretched springs, when they move around. In the case of the boy sliding down hill, he is giving the individual atoms in his bum and the ground more internal energy all the time, supplied by the potential energy gained from sliding down the hill.

19. Efficiency This is a measure of how good a “machine” is at transferring energy from the type supplied to the type wanted. The less is wasted the more efficient it is! A car is apparently only 25% efficient as it wastes ¾ of the energy in the petrol as heat and sound! Therefore not all the energy supplied is used for the intended purpose. The most efficient machine is supposedly a person cycling uphill in the correct gear!

20. energy or power To calculate efficiency either in terms of energy or power you use the following equation. % Efficiency = Useful output * 100% total input total input

21.  WEP Support  Calculation sheet 5