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PHYSICS REVIEW

PHYSICS REVIEW. BIG IDEAS. Energy cannot be created nor destroyed . Energy is converted from one form to another. An object that has energy can do work . Work is done when energy is transferred from one object to another or changed from one form to another.

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PHYSICS REVIEW

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  1. PHYSICSREVIEW

  2. BIG IDEAS • Energy cannot be created nor destroyed. Energy is converted from one form to another. • An object that has energy can do work. • Work is done when energy is transferred from one object to another or changed from one form to another. • The rate at which this energy is transferred or converted is called power.

  3. POTENTIAL ENERGY • Energy is stored, ready to act • e.g. Gravitational PE, Elastic PE • GPE= mass x gravity x height • weight x height • Force x distance = Work • GPE = gravitational potential energy (J) • m = mass (kg) g = gravity 10 (m/s/s) • h = height (m) • KINETIC ENERGY • Energy due to movement • e.g. Heat, Sound, Light, Mechanical • Kinetic Energy = 1/2 the product of • the mass times the square of the velocity • KE = mv2/2 • KE = kinetic energy (J) • m = mass (kg) • v = velocity (speed) (m/s) • WORK • Force exerted on an object making it • move through a distance • occurs with energy transfer • Work = Force x distance W = F x d • W = work (J) • F = force (N) • d = distance (m) • POWER • Amount of work per unit of time • Tells how fast energy is transferred • Power = Work/time P = Fd/t • P = power (watts) • W = work (J) • t = time (sec)

  4. ESSENTIALQUESTIONS In playground design (swings), what would be the perfect swing height for an optimum swing time? Whenever energy seems to disappear, where does it go? Do you do more work going straight up a mountain or taking the longer scenic route around to the top?

  5. Grade 8 Work, Energy, Power • Students should be able to: • Define potential and kinetic energy. • Use the terms kinetic and potential energy. • Show some understanding of energy of motion and energy of position. • Identify situations in which potential energy is stored. • Describe how potential energy is stored and how it is released. • Relate kinetic energy to mass/speed. • Identify when kinetic energy is converted to potential energy and vice versa. e.g. waterfall, rollercoaster • Recall and use the expressions KE.= ½mv2 and GPE = mgh. • Use the joule as the unit of energy / work. • Apply the principle of energy conservation to simple examples. • Define Work. • Describe processes by which energy is converted from one form to another. • Relate, without calculation, work done to the magnitude of a force and distance moved. • Describe energy transfer in terms of work done and make calculations involving Work = Force x distance.

  6. SUMMARY OF CONCEPTS: • If h is doubled, the GPE is doubled. • If H is tripled, the GPE is also tripled. • If speed (velocity) is doubled (2x), the Kinetic Energy increases (4x or 22). • If speed (velocity) is tripled (3X), the KE increases9x or 32. • The GPE at the top changes to KE at the bottom. GPE = w x h or GPE = mgh

  7. ENERGY A BODY HAS BECAUSE OF ITS POSITION OR CONDITION P.E.= Ep = mgh G.P.E. = weight x height

  8. Gravitational Potential Energy Depends on height

  9. Elastic Potential Energy Associated with objects that can be stretched or compressed

  10. PE = m g h Energy is transferred, WORK is done. E k = ½ m v2

  11. POTENTIAL ENERGY Ep or p.e. is the potential energy an object has because of its height. “The higher an object is lifted, the greater its p.e.” “The greater the mass of an object the greater its p.e.” the gain in p.e. = work doneEp = W

  12. gain in p.e. = work done Ep = W Remember: W = F x d where the lifting force is m x g (F= ma) (m = mass, g = acceleration due to gravity)

  13. Putting these formulae together: Gain in Potential energy= work done lifting Ep = W = lifting force x distance lifted (height)Ep = F x d (h) = weight force x distance lifted Ep = Fg x d (h) (g = 10N/kg) = mass of object x g x distance liftedEp = mgh

  14. KINETIC ENERGY (Ek) = ½ mv2 Kinetic energy equals 1/2 the product of the mass times the square of the velocity

  15. KINETIC ENERGY • Kinetic energy Ek or k.e. is the • energy that an object has because it • is moving • The unit of measure for k.e. is joule • The greater the mass of a moving • object, the greater the k.e. of the • object • if the mass doubles and the speed • stays the same, the Ek will double

  16. Potential Energy = Weight x Height (P.E. = w x h) or Ep= mgh Kinetic Energy = ½ Mass x Velocity2 (K.E.= 1/2mv2) weight = mg Units: Energy = joules (J) Weight = newtons (N) Mass = kilograms (kg) Velocity = m/s Height = meters (m) Gravity constant = 9.8m/sec/sec Work = joules 1km = 1000m 1kg= 1000g 1hr= 3,600sec

  17. Working with Forces FORMULAE Constant: Acceleration due to gravity 9.8 m/sec/sec F = MA W= mg

  18. Weight and Mass Weight is a measure of the force of gravity on an object Weight = Mass x acceleration due to gravity w= mg

  19. Mass kilogramsAcceleration m/sec/secforce newton (N) Unit of Force 1N = 1 kg x 1 m/sec/sec

  20. WORK A force acting through a distance Work = Force x Distance

  21. FORCE DISTANCE Work = force x distance W = F d Work = F (N) x D (m) = Newton-meter or joule (J)

  22. Investigating Conservation of Energy PE  KE  Building  work done Will all the PE be converted to KE  work ? Aim: To investigate how an increase in height of a wrecking ball affects the work done. How will we measure it (work done)? Will all of the potential energy (PE) be converted to work? SUMMARY: 1. An increase in height (GPE) will lead to an increase in work done (PE=W) 2. The amount of energy gained (PE) decreases as it gets converted or transformed due to energy loss (e.g. heat, air resistance, deformation).

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