Work, Power, and Energy: Unleashing the Forces

Work, Power, and Energy

Understanding the forces that drive our world

Work: Force x Displacement

Work is done when a force causes an object's displacement. The force and direction of movement must be parallel. Work = Force x Displacement. The unit for work is Joules (J).

Multiple Choice

What is the unit for work?

• Joules (J)

• Meters (m)

• Newton (N)

• Watts (W)

Unit for Work: Joules (J)

Joules (J) is the unit used to measure work. Work is defined as the amount of energy transferred by a force over a distance. It is named after James Prescott Joule, a British physicist.

Work, Power, and Energy

Work, power, and energy are fundamental concepts in physics.

Work is the product of force and displacement, and can be positive or negative depending on the direction of the force.

Power is the rate at which work is done, while energy is the capacity to do work.

Multiple Choice

Which of the following is the rate at which work is done?

• Force

• Displacement

• Power

• Energy

Power

Trivia: Power is the rate at which work is done. It measures how quickly work is being done or energy is being transferred. It is calculated by dividing the amount of work done by the time taken to do it.
Power is measured in watts (W).

Work, Power, and Energy

Work is negative (-) when force is opposite that of motion.

For angles more than 90° but less than 270°, use cosine and inverse sine.

Positive (+) work speeds up the car, while negative (-) work slows it down.

Math Practice:
If 2.0 J of work is done to move a 180g apple, what is the vertical displacement?
W = FΔX
2.0J = 1.8 kg (Δx)
2.0/1.8 = Δx
Δx = 1.1 meters

Multiple Choice

What is the relationship between work and force when the force is opposite to the motion?

• Work is positive (+)

• Work is negative (-)

• Work is zero (0)

• Work is undefined

Work and Force

Trivia: When the force is opposite to the motion, the work is negative (-). This means that the object is losing energy as it moves. It's like pushing a heavy box uphill, where you have to do work to overcome the force of gravity pulling it down.

Multiple Choice

What formulas can be used to calculate work done on weights and work done while pushing a cart?

• W = F ⍙X and

  W = F ⍙X Cosθ

• W = F⍙X and

  W = F⍙XSinθ

• W = FX and

  W = F⍙X Tanθ

• W = FX and

  W = FX θ

Work Formulas

Did you know?
The work done on OBJECTS can be calculated using the formula
W = FΔX while the work done while pushing a cart can be calculated using the formula W = FΔX Cosθ. W use the formula that has an angle for problems that are not perfectly horizontal.
These formulas help us understand the amount of work done in different scenario.

Multiple Choice

Energy stored from position, stress, electrical charge, or others.

• Potential

• Kinetic

Multiple Choice

Energy of motion.

• Mechanical

• Electrical

• Kinetic

Multiple Choice

Energy that comes from breaking and reforming atomic bonds.

• Nuclear

• Chemical

• Atomic

Multiple Choice

Energy that comes from the motion of atoms.

• Sound

• Heat

• Light

Multiple Choice

Energy that travels as a stream of electrons.

• Chemical

• Nuclear

• Electrical

Multiple Choice

Energy that travels through solids, liquids, and gases as vibrations, but can't travel through space.

• Light

• Sound

• Nuclear

Multiple Choice

Energy stored in the nucleus of an atom.

• Nuclear

• Chemical

• Light

Multiple Choice

Energy of moving parts that is the sum of all PE & KE.

• Mechanical

• Compound

• Machine

WORK

• In physics, WORK is when energy is transferred to or from an object.

• Work is done when FORCE is applied to move an object or its atoms through a PUSH or a PULL over a DISTANCE.

Multiple Choice

Two equal mass marbles are at the top of a ramp. One marble falls to the ground off the back while the other rolls down the ramp. What is true about the marbles when they reach the ground?

• The marble that rolled down the ramp is moving faster than the marble that fell.

• The marble that fell down the back of the ramp is moving faster than the marble that rolled.

• The marble that rolled down the ramp is not moving when it reaches the ground.

• The two marbles are moving with the same speed.

Explanation Slide...

They both started off with equal potential energy.They both wound up with zero potential energy.They both would have converted the same amount of potential energy into kinetic energy.They both would have the same speed for the same kinetic energy.

Multiple Choice

A crane lifts an 8-m long steel girder weighing 2600 N up 15 m off the ground. The crane did ___ of work.

• 0 J

• 39000 J

• 20800 J

• 2600 J

Explanation Slide...

The block starts with some potential energy, and no kinetic energy.The block winds up with less potential energy, and no kinetic energy.The energy of the system changed; there was a negative change in the energy.The change in energy of a system is the work done on the system by external forces.Negative work must have been done by friction or drag or other non-conservative forces.

Multiple Choice

A block starts at rest at point P at the top of a ramp which is height h above the ground. The block slides down one side and up the other, stopping at a point less than h above the ground.

• The block did not go as high on the other side because gravity pulls down.

• The block did not go as high on the other side because potential energy always has to decrease.

• The block did not go as high on the other side because work from friction made the mechanical energy less.

• The situation as described is impossible to happen.

Explanation Slide...

Potential energy can turn into kinetic energy, and kinetic energy can turn into potential energy.The point with the most kinetic energy would be the point with the least potential energy.The point with the least potential energy would be the lowest point.

Multiple Choice

If there is no friction on this track, at which point would the coaster have the most kinetic energy?

• A

• B

• C

• D

Multiple Choice

Where is the roller coaster gaining potential energy?

• A to B

• B to C

• C to D

• The roller coaster is always losing potential energy

Multiple Choice

A 40-kg person is climbing 3 m up a flight of stairs in 6 seconds. How much work did they do climbing the stairs?

• 400 J

• 1200 J

• 200 J

• 120 J

Explanation Slide...

W = F Δ x

The force is the force of gravity:
F = mg
(Use 10 m/s² for g if you're in a hurry)

Multiple Choice

A 40-kg person is climbing 3 m up a flight of stairs in 6 seconds. How much power did they exert climbing the stairs?

• 400 W

• 1200 W

• 200 W

• 120 W

Explanation Slide...

P = W / Δt

W = F Δx

The force is the force of gravity:
F = mg(Use g = 10 m/s² if you're in a hurry)