Presentation on theme: "Energy. Which has more energy? Explain. Work Work ( W ) - a force acting upon an object to cause a change in position and a change of energy. Units Nm."— Presentation transcript:
Work ( W ) - a force acting upon an object to cause a change in position and a change of energy. Units Nm = Joules (J) W = Fd = ∆ E t
If a box lifted 5m gains 100J of energy, 1) What force was used? F d = ∆E T 2) What was the work done on the box? w = ∆E T
If a box lifted 5m gains 100J of energy, 1) What force was used? F 5m = 100J 2) What was the work done on the box? w = 100J
If a box lifted 5m gains 100J of energy, 1) What force was used? F = 20N 2) What was the work done on the box? w = 100J
Are the following scenarios examples of work? Explain why or why not.
Can vertical forces produce horizontal work? Explain. NO! A vertical force can never cause a horizontal displacement; a vertical force does not do work on a horizontally displaced object!! Independence of perpendicular vectors.
Positive WorkNegative Work Force is in the same direction as motion. Increases energy of object. Force opposes motion. Decreases energy of object.
When the force causing a change in position is acting at an angle compared to the direction of movement, you must: Resolve the force into components. Use the force that is acting in the same direction as the displacement. Work at Angles
Energy can neither be created nor destroyed. It can only be transformed or transferred from one form to another within a closed system. The total mechanical energy within a closed system will always remain the same. Energy Conservation Principle in Ideal Mechanical Systems
E t = PE + KE + Q E i = E f * Not on Reference Table
Using a Pie Chart to Understand Conservation of Energy Size of Circle represents total energy remains the same size in a closed system
Using a Pie Chart to Understand Conservation of Energy Size of Slices represents specific types of mechanical energy red = Kinetic blue = Gravitational Potential green = Thermal orange = Elastic Potential
Do NOT affect the total mechanical energy of a system. F grav F spring Internal Forces
Increase or decrease the total mechanical energy of a system. F app F fric F air F tens F norm External Forces
When work is done upon an object by an external force, the total mechanical energy (KE + PE) of that object is changed. W = ΔE T = E f - E i Work Energy Theorum * Already on page 128
If the work is "positive work", then the object will gain energy. If the work is "negative work", then the object will lose energy. The gain or loss in energy can be in the form of potential energy, kinetic energy, or both. Work Energy Theorum
Pendulums While at Pisa, Galileo was also inspired to study pendulums. Galileo was sitting in the pews of a cathedral, gazing upwards, when he noticed that one of the great lamps was swinging back and forth. He noticed that the swing of the lamp was incredibly regular. This motivated him to study pendulums.
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