NIS – PHYSICAL SCIENCE

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Lecture 15The Nature of Energy

Ozgur Unal

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EnergyWhat is work?

Examples:An apple on a tree has the ability to cause a change if it falls down, so it has energy.The sunlight has the ability to cause a change (tanning), so it has energy.Heat has the ability to cause a change (cooking food), so it has energy.

Energy is the ability to do work.Or, energy is the ability to cause a change.The ball in Figure 1 is moving and it has the ability to break the window glass.

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Different Forms of Energy

Energy can take different forms:Thermal energyRadiant energyChemical energy stored in foods and fuelsElectrical energy etc.

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Kinetic EnergyEnergy due to motion is called kinetic energy.Every moving object has kinetic energy.

Which object would cause a greater change?1- A light object or a heavy object moving at the same speeds?2- Two same objects moving as different speeds?A heavy object has more kinetic energy than a light object moving at the same speed.A faster object has more kinetic energy than a slower object with the same mass.

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Kinetic EnergyKinetic energy:

KE = m * v2 / 2The unit of energy is Joule (J). Express joule in terms of base units.Is energy a vector?

Example: What is the kinetic energy of a baseball moving at a speed of 40 m/s if the baseball has a mass of 0.15 kg?

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Potential EnergyEnergy doesn’t have to involve motion.Stored energy due to position is called potential energy.An object with a certain height has the potential to cause a change if it start falling down.

Examples for potential energy:Elastic potential energy is energy stored by something that can stretch or compress.Observe the springs given to youand explain how energy can bestored in it.

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Potential EnergyExamples for potential energy:Foods and fuels contain stored energy in chemical bonds.Energy stored in chemical bonds is called chemical potential energy.Check out Figure 3!Energy is stored in the bonds that hold the carbon and hydrogen atoms together and is released when the gas is burned.

NIS – PHYSICAL SCIENCE

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Lecture 16Gravitational Potential Energy

Ozgur Unal

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Gravitational Potential EnergyAnything that can fall has stored energy called gravitational potential energy (GPE).

GPE = m * g * hWhat is the unit of GPE?Is GPE a vector?

Example: Find the height of a baseball with a mass of *.15kg that has a GPE of 73.5 J.

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Gravitational Potential EnergyWhich object has the greatest potential energy?