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# Work, power and energy

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• 1. By iTutor.com T- 1-855-694-8886Email- info@iTutor.com
• 2. The Law of Conservation of Mass The Law of Conservation of Matter (or Mass) states that matter cannot be created nor destroyed in an ordinary chemical reaction. No atoms are gained or lost in a reaction; they are just rearranged. The total mass of reactants = Total mass of products
• 3. WorkWork is the transfer of energy through motion. Inorder for work to take place, a force must be exertedthrough a distance.The amount of work done depends on two things: The amount of force exerted The distance over which the force is applied. Direction of movement as result of ForceDirection of Force Object
• 4. Work If you push a box with a force of one Newton for a distance of one meter, you have done exactly one joule of work.
• 5. Work (force is parallel to distance) Force (N)Work (joules) W=Fxd Distance (m)
• 6. Work (force at angle to distance) Force (N)Work (joules) W = F d cos  Angle Distance (m)
• 7. Work done against gravity Mass (g) Height objectWork (joules) raised (m) W = mgh Gravity (m/sec2)
• 8. Power Power is defined as the rate at which work is done. It can also refer to the rate at which energy is expended or absorbed. Power is equal to the amount of work done divided by the time it takes to do the work. Power (W) Change in work or energy (J) P = E t Change in time (sec)
• 9. PowerA unit of power is called a watt.Another unit horsepower.One horsepower (the avg power output of a horse) is equal to 746 watts.
• 10. PowerAnother way to express power is as a multiple of force and its velocity, if the velocity and force are both vectors in the same direction. Power (W) P=F.v Velocity (m/sec) Force (N)
• 11. Efficiency Efficiency can also mean the ratio of energy output divided by energy input. Energy output (J) Efficiency Eo e= EiEnergy input (J) Wout work done with no friction (often m g h) eff = = work actually done by input force Win Copyright reserved. © 2012 The E Tutor
• 12. Efficiency  Efficiency is defined for a process.  A process is any activity that changes things and can be described in terms of input and output.  The efficiency of a process is the ratio of output to input. Efficiency – 10%
• 13. Energy flow in systemsEnergy flows almost always involve energy conversions.To understand an energy flow: 1. Write down the forms that the energy takes. 2. Diagram the flow of energy from start to finish for all the important processes that take place in the system. 3. Try to estimate how much energy is involved and what are the efficiencies of each energy conversion.
• 14. Energy flow in human technologyThe energy flow in technology can usually be broken downinto four types of processes: 1. Storage ex. batteries, springs, height, pressure 2. Conversion ex. a pump converting mechanical energy to fluid energy 3. Transmission ex. through wires, tubes, gears, levers 4. Output ex. heat, light, electricity
• 15. Energy flow The energy flow diagram for a rechargeable electric drill shows losses to heat or friction at each step.
• 16. Energy flow
• 17. www.iTutor.comThe End