Potential energy (PE) or Kinetic energy (KE) All energy can be in one of two forms:
Potential energy is stored energy-- energy ready to go. Examples: A lawn mower filled with gasoline, a car on top of a hill, and students waiting at a bus stop are all examples of potential energy.
Types of potential energy include: Gravitational potential energy- energy related to an object’s height Elastic potential energy- energy associated with objects being stretched (like a rubber band) or compressed (like a spring)
Gravitational Potential Energy The rock climbers have gravitational potential energy
Elastic Potential Energy The energy stored in a stretched object, such as the trampoline, is elastic potential energy. Rank the amount of elastic potential energy of the trampoline from greatest to least
Types of potential energy Which is elastic and which is gravitational? Which is elastic and which is gravitational?
Most of the energy under our control is in the form of potential energy. Potential energy can be viewed as motion waiting to happen. When the motion is needed, potential energy can be changed into kinetic energy.
Kinetic energy is energy at work-- energy of motion Examples: A lawn mower cutting grass, a car racing down a hill, and students running home from school are examples of kinetic energy.
Factors that affect KE include: Speed- the faster an object moves, the more kinetic energy it has Mass- kinetic energy increases as mass increases
Kinetic Energy The kinetic energy of an object depends on its speed and mass. Greatest KE More mass more speed 2 nd Greatest KE-- More Mass, Not as much speed Least KE- Least mass, same speed as blue
Which has more kinetic energy, a bird or a plane? Why? A plane has more kinetic energy than a bird because it moves faster and has a greater mass.
We have often heard phrases like, "Conserve energy; turn off the lights." To scientists, conservation of energy is something entirely different.
The Law of Conservation of Energy states that the total amount of energy in a system remains constant ("is conserved") before and after a transformation….so in other words, energy cannot be created or destroyed.
That's really what we mean when we say we are "using" energy. The law of conservation of energy means that when energy is being used, it is not being used up. Instead, it is being changed from one form into another. Transformation between potential and kinetic energy is one of the most common energy transformations.
In which position does the girl have the greatest PE?position In which position does the girl have the greatest KE?
In which position does the girl have the greatest PE? A In which position does the girl have the greatest KE? B
Describe each position: A The ball has great KE when it is thrown
Describe each position: B The ball’s PE is maximum
Describe each position: C The ball is reaching max KE
Describe each position: D The ball is losing PE & gaining KE again
A pendulum is a perfect object to use to show the transfer of PE to KE to PE to KE to PE to KE to PE to KE to PE to KE…get the picture? picture
Figure 1: Illustration of potential energy being converted into kinetic energy using water; Here, the kinetic energy is in the form of gravity accelerating water, which could be rapids, cascades, or even a waterfall!
Figure 2: Illustration of potential energy being converted into kinetic energy using a roller coaster; Here, the kinetic energy is in the form of a zooming roller coaster moving fast enough under the influence of gravity to make it through the 360-degree loopgravity
Do you know why the first hill of a roller coaster always has to be the tallest?first hill
Some energy is transformed to thermal energy so the ride does not have enough energy to make it up a hill that tall again. So what is thermal energy?
All substances are made up of small particles called atoms. Atoms are in constant motion.
Thermal energy is the total energy of all particles in an object. Thermal energy is a form of KE.
The amount of thermal energy depends upon the following: Temperature of object- the higher the temperature = more thermal energy Number of particles- more particles (mass) = more thermal energy
How should the bottom diagram be completed to show three pies with more thermal energy than the first? In the top two diagrams, which chicken pot pie contains more thermal energy? Higher Temperature More Particles More particles 200 Higher Temp 300 More Particles 200
Heat is the transfer of thermal energy from a warmer object to a cooler object (always in this direction!)
The warm object cools down & the cooler object warms up until their temperatures are equal. Demonstration here
There are three methods of energy transfer: transfer
ConductionConduction- the transfer of heat from one particle to another within an object or between two objects. Examples: touching the handle of a hot pan, holding an ice cube in your hand, cooking an egg in a frying pan, and standing on the hot beach sand
ConvectionConvection- the transfer of heat in fluids, such as air and water, using convection currents Examples: warming your hands by the fire place, heating a can of soup on the stove, and heating your home
Radiation- the transfer of energy by electromagnetic waves. RadiationRadiation doesn ’ t require matter (atoms) to travel through. Examples: Sun’s energy traveling through empty space and feeling the heat on your face at a bonfire
As thermal energy increases, particles spread out causing substances to expand, this is known as thermal expansion.
Conductors- materials that conduct heat well, i.e. metals Insulators- materials that do NOT conduct heat well, i.e. wool and Styrofoam
Heat transfer goes on all around you all the time, even on the beach.