GPE and Kinetic Energy

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  • GPE and Kinetic Energy

    1. 1. Gravitational Potential and Kinetic Energy GCSE Physics
    2. 2. Learning Intentions <ul><li>By the end of the lesson we will be able to… </li></ul><ul><li>State how Work Done and GPE are linked </li></ul><ul><li>Recall the equations for calculating Potential and Kinetic energy </li></ul><ul><li>Solve some simple problems related to GPE and Kinetic energy </li></ul>
    3. 3. What is Gravitational Potential Energy (GPE) ? <ul><li>An object lifted up vertically has the ability to fall back to its original position, it has the potential to move . We say the object has gained GPE . </li></ul>Page 13
    4. 4. GPE in action…
    5. 8. GPE linked to Work Done <ul><li>Consider the stone lifted up- what is the work done on the stone? </li></ul><ul><li>Wd = F x d </li></ul><ul><li>= (2 x 10) x 5 </li></ul><ul><li>= 100 J </li></ul><ul><li>This is also equal to potential energy gained by the stone. </li></ul>5 m 2 kg
    6. 9. Equation for GPE <ul><li>GPE = Weight x Height above the ground </li></ul><ul><li>Joules (J) = Newton (N) x metre (m) </li></ul><ul><li>Important Note- it is the height lifted against gravity that matters </li></ul>5 m 2 kg Word Equation Units
    7. 10. Newton’s Cradle <ul><li>Newton’s cradle can help us understand the factors that effect GPE </li></ul><ul><li>If we increase the height the ball is released from, what will happen to show that the GPE has also increased? </li></ul><ul><li>When we lift up more than one ball and release them what happens? </li></ul><ul><li>Which factor does this show effects GPE? </li></ul>
    8. 11. What is Kinetic Energy? <ul><li>Any object which is in motion has kinetic energy. </li></ul>Speed around the Sun – 107 000 km/hr or 66 500 mph
    9. 12. Fastest man on the planet over 100 metres 10.32 m/s or 23.1 mph
    10. 13. What does KE depend on? <ul><li>Consider a flying pig heading towards you- if you had to stop the pig what two factors (or variables) would you be concerned about? </li></ul><ul><li>The speed it is moving towards you </li></ul><ul><li>The mass of the pig </li></ul>
    11. 14. Equation for KE <ul><li>Kinetic Energy = ½ x Mass x Speed 2 </li></ul><ul><li>KE = ½ x m x v 2 </li></ul><ul><li>Joules = kg x metre/second </li></ul>Word Equation Units Dimensions
    12. 15. KE linked to Work Done <ul><li>Consider a stone of mass m kilograms, increasing in speed from 0 to v m/s in time t seconds </li></ul><ul><li>Work Done = Force x Distance </li></ul><ul><li>Force = Mass x Acceleration </li></ul><ul><li>= m x (v / t) </li></ul><ul><li>Distance = Average Velocity x Time </li></ul><ul><li>= ½ v x t </li></ul><ul><li>Work Done = m x (v / t) x ½ x v x t </li></ul><ul><li>= ½ x m x v 2 </li></ul><ul><li>Kinetic Energy = Work Done= ½ x m x v 2 </li></ul>t = 0 t = t v 0
    13. 16. Example Question on KE <ul><li>What is the KE of a football of mass 0.4 kg moving at a speed of 10 m/s? </li></ul><ul><li>KE = ½ x m x v 2 </li></ul><ul><li>= 0.5 x 0.4 x 10 2 </li></ul><ul><li>= 20 J </li></ul>
    14. 17. Back to Earth… <ul><li>Mass is 5.98 x 10 24 kg </li></ul><ul><li>Speed is 30 000 m/s </li></ul><ul><li>KE = ½ x m x v 2 </li></ul><ul><li>= 0.5 x (5.98x10 24 ) x 30 000 2 </li></ul><ul><li>= 26.9x10 32 J </li></ul>26 900 000 000 000 000 000 000 000 000 000 000 J
    15. 18. Your turn… <ul><li>Page 16 </li></ul><ul><li>Try question 25 </li></ul>
    16. 19. Learning Intentions <ul><li>By the end of the lesson we will be able to… </li></ul><ul><li>Recall how Gravitational Potential and Kinetic energy are linked </li></ul><ul><li>Solve some simple problems relating GPE and Kinetic energy </li></ul><ul><li>State how to calculate the efficiency of a system </li></ul>
    17. 20. Conservation of Energy <ul><li>Energy cannot be made or destroyed but it can change form, total energy stays constant </li></ul><ul><li>Consider a marble at the top of a ramp with 2.5 J of energy… </li></ul>GPE = 2.5 J KE = 0 J GPE = 0 J KE = 2.5 J GPE = 1.25J KE = 1.25 J Total Energy- 2.5 J 2.5 J 2.5 J a b c c b a Ignoring heat energy losses!
    18. 21. Conservation of Energy <ul><li>When a falling object ‘loses’ GPE it is transformed to KE ‘gained’ </li></ul>GPE lost = KE gained
    19. 22. Example Question <ul><li>A stone of mass 3 kg is dropped from a height of 60 cm onto the ground. </li></ul><ul><li>a) Calculate its GPE before it is dropped </li></ul><ul><li>b) When it hits the ground how much GPE does it have? How much KE does it have? </li></ul><ul><li>c) At what speed will it hit the ground? </li></ul>
    20. 23. Answer <ul><li>GPE = Weight x height </li></ul><ul><li>= (3 x 10) x 0.6 </li></ul><ul><li>= 18 J </li></ul><ul><li>b) GPE is zero as its height off the ground is zero. KE is 18 J, all the GPE has been converted into KE </li></ul><ul><li>c) KE = ½ x m x v 2 </li></ul><ul><li>18 = ½ x 3 x v 2 </li></ul><ul><li>12 = v 2 </li></ul><ul><li>3.46 m/s = v </li></ul>
    21. 24. Question Time <ul><li>Page 16 Question 27 </li></ul><ul><li>GPE = Weight x height </li></ul><ul><li>KE = ½ x m x v 2 </li></ul><ul><li>GPE lost = KE gained </li></ul><ul><li>total energy stays constant </li></ul>

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