EQ: What type of energy describes the motion of a system?

The word energy is used in many different ways in everyday speech. Some fruit-and-cereal bars are advertised as energy sources. Athletes use energy in sports. Companies that supply your home with electricity, natural gas, or heating fuel are called energy companies. The Many Forms of Energy

Scientists and engineers use the term energy much more precisely. Work causes a change in the energy of a system. That is, work transfers energy between a system and the external world. The Many Forms of Energy

When work is done on a system, the energy of that system increases. On the other hand, if the system does work, then the energy of the system decreases. The Many Forms of Energy

 Mechanical energy is the energy that is possessed by an object due to its motion or due to its position.  The total mechanical energy of a system is the sum of the PE and KE of a system  Mechanical energy can be either kinetic energy (energy of motion) or potential energy (stored energy of positionkinetic energypotential energy

What is causing the ball to move in the other direction? What would happen to the one side of the ball if the other ball was lifted higher to begin the motion? Why? Hmm?!

Kinetic energy exists whenever an object which has mass is in motion with some velocity. Everything you see moving about has kinetic energy. The greater the mass or velocity of a moving object, the more kinetic energy it has.

Formula: KE = ½ m v 2 QuantityVariableUnit Kinetic Energy KEJoules (J) massmKilograms (kg) velocityvMeters/second (m/s)

Silvana Cruciata from Italy set a record in one-hour running by running km in h. If Cruciata’s kinetic energy was 694 J, what was her mass?

Example continuation Givens: Δx = km = × 10 4 m Δt = h = × 10 3 s KE = 694 J Unknown: mass Equation(s): manipulated Substitution: v = × 10 4 m/3.600 × 10 3 s = m/s m = 2(694)/(5.023) 2 = Solution: m = 55.0 kg

Ability to do work by virtue of position or condition. In other words, the amount of work the object capable of doing based on its position. A stretched bowA suspended weight

Two Types of Potential Energy:  Gravitational Potential Energy (GPE): The energy associated with an object due to the object’s position relative to a gravitational source.  Elastic Potential Energy: The energy stored in a compressed or stretched spring.

QuantityVariableUnit Potential EnergyPEJoules (J) MassMKilogram (kg) height∆yMeters (m) gravitygMeters/second (m/s 2 ) Formula: PE = m g h

In 1993, Javier Sotomayor from Cuba set a record in the high jump by clearing a vertical distance of 2.45 m. If the gravitational potential energy associated with Sotomayor at the top point of his trajectory was 1.59 x 10 3 J, what was his mass? m = 66.2 kg

QuantityVariableUnit Potential EnergyPEJoules (J) Spring constantkNewton/meter (N/m) Distance compressed or stretched xMeters (m) Formula: PE elastic = ½ kx 2

A 70.0 kg stuntman jumps from a bridge that is 50.0 m above the water. Fortunately, a bungee cord with an unstretched length of 15.0 m is attached to the stuntman, so that he breaks his fall 12.0 m above the water’s surface. If the total potential energy associated with the stuntman and cord is 3.43 x 10 4 J,what is the force constant of the cord?

Example continuation: Givens: m = 70.0 kg h = 12.0 m x = 50.0 m − 12.0 m − 15.0 m = 23.0 m PEg = 0 J at river level PEtot = 3.43 × 104 J g = 9.81 m/s2 Unknown: k Equation(s): PEtot = PEg + PEelastic Petot = mgh + 1/2kx 2 manipulated

The change in gravitational potential energy of an object is equal to the amount of work needed to change its height Therefore: Work =  PE Fd = mgh

The KE of a moving object is equal to the work the object is capable of doing while being brought to rest Therefore: W =  KE Fd = ½mv 2

A forward force of 11.0 N is applied to a loaded cart over a distance of 15.0 m. If the cart, which is initially at rest, has a final speed of 1.98 m/s, what is the combined mass of the cart and its contents?

Putting these two ideas together gives us the general Work-Energy Theorem: If no change in energy occurs, then no work is done. Therefore, whenever work is done, there is a change in energy.

Closing Task Show your knowledge of how kinetic and potential energy are converted from one form to the other by labeling the amount of KE and PE on the illustration at various points. Sketch it into your notebook