The ability to cause change or do work. It appears in many forms (kinetic, potential, thermal, chemical, etc.) but is conserved in total.

Energy of motion. Moving objects (like cars or rolling balls) have kinetic energy; faster or more massive objects have more.

Energy transferred when a force causes an object to move in the direction of the force. In simple cases, work = force × distance and is measured in joules (J).

A rigid bar that pivots on a fulcrum to multiply force or change its direction.

The rate at which work is done or energy is transferred; measured in watts (W).

The ability to cause change or do work; appears in many forms such as kinetic, potential, thermal, and chemical.

Energy, Work, and Simple Machines — SHS Science Foundations: Integrated Chemistry, Biology, and Physics

Energy Everywhere: Big Picture

Energy: The Big Idea

Energy is the "currency" of motion and change. Whenever something moves, heats up, lights up, or changes, energy is involved. It connects to the forces and motion you learned about earlier.

Conservation of Energy

Key rule: Energy is never created or destroyed; it only changes form. This is the law of conservation of energy. Total energy stays constant, but it can move and transform.

Common Forms of Energy

Everyday forms: kinetic (motion), gravitational potential (height), elastic potential (stretched/compressed), chemical (food, fuel), thermal (heat), electrical and light (circuits, the Sun).

Energy Chains

Real-life situations mix forms of energy. Example: food (chemical) → muscles move (kinetic) → backpack is lifted (gravitational potential) → body warms up (thermal).

What You Will Learn

You will track energy transformations, learn work and power, and see how simple machines like ramps and pulleys change how we apply force and distance to get jobs done.

Forms of Energy and Transformations

Kinetic and Gravitational Energy

Kinetic energy is energy of motion. Faster or heavier objects have more. Gravitational potential energy is stored because of height, like water behind a dam or a book on a shelf.

Elastic and Chemical Energy

Elastic potential energy is stored in stretched or compressed objects, like springs or rubber bands. Chemical energy is stored in bonds, like in food, gasoline, and batteries.

Thermal, Electrical, and Light

Thermal energy is the random motion of particles; hotter means more. Electrical and light (radiant) energy appear in circuits, screens, and sunlight.

Energy Transformations

Devices transform energy: hair dryer (electrical → thermal + sound), car engine (chemical → kinetic + thermal + sound), dam (gravitational → kinetic → electrical → light + thermal).

Friction and "Lost" Energy

Friction and resistance convert useful energy into thermal and sound energy. The total energy is still conserved, but less remains in the form you want for doing useful work.

Spot the Energy: Quick Thought Exercise

For each situation, identify at least two forms of energy and describe one transformation.

Riding a bike up a hill

What forms of energy are involved? Where does the energy come from and where does it go?

Charging your phone, then watching a video

While charging: which forms of energy are changing?
While watching: trace energy from the battery to your eyes and ears.

Dropping a ball onto a carpet

Just before it hits, what form of energy is largest?
After it stops, where did that energy go?

Write short answers like this:

"Bike: chemical in muscles → kinetic of bike → gravitational potential as I go higher + thermal in brakes and tires."

Try answering out loud or in a notebook. Focus on before vs. after and name the main energy forms.

Work: How Forces Transfer Energy

Physics Meaning of Work

In physics, work happens when a force causes an object to move in the direction of the force. Simple rule: Work = force × distance if the force is constant and along the motion.

Units of Work

Force is in newtons (N), distance in meters (m), so work is in joules (J). One joule is one newton acting over one meter: 1 J = 1 N·m.

No Movement, No Work

If you push hard on a wall and it does not move, you may feel tired, but in physics the work on the wall is zero: the distance is zero.

Direction Matters

Carrying a backpack at constant height: your force is mostly upward, motion is sideways. In basic physics we say you do almost no work on the backpack in the direction of motion.

Work Transfers Energy

Lifting a 5 N book by 2 m: work ≈ 5 N × 2 m = 10 J. That 10 J becomes gravitational potential energy. Work is one main way energy is transferred between objects.

Work and Power: Sample Calculations

What Is Power?

Power is how fast work is done: Power = work ÷ time. One joule per second is one watt (W). More power means the same work done in less time.

Backpack Example: Work

Backpack mass 5 kg → weight ≈ 50 N. Lift 1.5 m: work ≈ 50 N × 1.5 m = 75 J. That energy becomes gravitational potential energy.

Backpack Example: Power

Lift in 3 s: power = 75 J ÷ 3 s = 25 W. Lift in 1 s: power = 75 J ÷ 1 s = 75 W. Same work, but higher power when you do it faster.

Stairs Example: Work

You plus bag: 60 kg. Weight ≈ 600 N. Climb 3 m: work = 600 N × 3 m = 1800 J, all against gravity to gain height.

Stairs Example: Power

Walk up in 20 s: power = 1800 J ÷ 20 s = 90 W. Run up in 5 s: power = 1800 J ÷ 5 s = 360 W. Same work, but running requires more power.

Mini Calculation Challenge: Work and Power

Try these in your head or on paper. Round g to 10 m/s² to keep it simple.

Box lift

A 10 kg box is lifted straight up 0.5 m.
a) Estimate the force needed (use weight).
b) Calculate the work done on the box.
c) If the lift takes 2 s, what is the power?

Elevator ride

An elevator raises a 400 kg load by 5 m in 10 s.
a) Work done against gravity?
b) Power of the elevator?

Pause and calculate before checking:

Suggested answers (do not peek too early):

1a) ~100 N, 1b) ~50 J, 1c) ~25 W
2a) ~20,000 J, 2b) ~2,000 W

If your answers are different, check:

Did you use g ≈ 10 m/s²?
Did you multiply force × distance for work and work ÷ time for power?

Simple Machines and Mechanical Advantage

What Are Simple Machines?

Simple machines are basic devices like levers, pulleys, and inclined planes that help you do work by changing the size or direction of the force you apply.

No Free Energy

Simple machines do not create energy or reduce total work (ignoring friction). They let you trade force for distance: less force over more distance, or more force over less distance.

Mechanical Advantage

Mechanical advantage (MA) tells how many times a machine multiplies your input force. If MA > 1, you use less force but must move farther.

Lever Example

With a long crowbar, you push a long distance with small force to lift a rock a short distance with large force. Input distance is large, output distance small: the lever multiplies your force.

Pulley and Ramp Examples

A fixed pulley mostly changes direction (MA ≈ 1). Multiple pulleys can multiply force but require more rope. A ramp lets you use less force over a longer path instead of lifting straight up.

Compare: Lifting vs. Using a Ramp

Imagine you need to load a 100 kg crate into a truck bed 1 m high. Use g ≈ 10 m/s².

Lifting straight up

Force needed ≈ weight = ?
Distance moved = 1 m.
Work done = force × distance = ?

Using a 4 m long ramp (no friction, gentle slope)

The vertical height is still 1 m.
a) The work you must do (ignoring friction) is roughly the same as lifting straight up. Why?
b) To keep work the same but increase distance to 4 m, what must happen to the force you need?

Think qualitatively:

If work = force × distance stays about the same, and distance is 4 times bigger, the force can be about 4 times smaller.

Write a short explanation like:

"The ramp lets me push with less force because I move the crate over a longer distance. The total work is about the same, so energy is conserved."

Optional challenge: Sketch both situations and label force, distance, and work on your diagram.

Check Understanding: Energy, Work, and Machines

Answer this question to check your understanding of energy, work, and simple machines.

Which statement best explains how a simple machine like a ramp can make lifting a heavy box easier, without breaking the law of conservation of energy?

The ramp creates extra energy, so you do less work overall.
The ramp lets you use a smaller force over a longer distance, so the total work done is about the same.
The ramp reduces the weight of the box, so no work is needed.
The ramp increases power by making you do the same work in less time.

Show Answer

Answer: B) The ramp lets you use a smaller force over a longer distance, so the total work done is about the same.

A ramp is a simple machine that trades force for distance. You apply a smaller force but over a longer path. Because work ≈ force × distance, the total work (and energy change) stays about the same, so energy is conserved.

Key Term Review: Energy, Work, Power, Machines

Use these flashcards to review the main ideas from this module.

Energy: The ability to cause change or do work. It appears in many forms (kinetic, potential, thermal, chemical, etc.) but is conserved in total.
Law of conservation of energy: Energy cannot be created or destroyed; it can only be transferred or transformed from one form to another. Total energy stays constant.
Kinetic energy: Energy of motion. Moving objects (like cars or rolling balls) have kinetic energy; faster or more massive objects have more.
Gravitational potential energy: Energy stored due to an object's height in a gravitational field. Higher positions have more gravitational potential energy.
Work (physics): Energy transferred when a force causes an object to move in the direction of the force. In simple cases, work = force × distance and is measured in joules (J).
Power: The rate of doing work or transferring energy. Power = work ÷ time and is measured in watts (W), where 1 W = 1 J/s.
Simple machine: A basic device (like a lever, pulley, or inclined plane) that helps you do work by changing the size or direction of the force you apply.
Mechanical advantage: A measure of how much a machine multiplies your input force. If mechanical advantage > 1, you use less force but move a greater distance.

Key Terms

work: In physics, the energy transferred when a force causes an object to move in the direction of the force; equal to force × distance in simple cases.
lever: A rigid bar that pivots on a fulcrum to multiply force or change its direction.
power: The rate at which work is done or energy is transferred; measured in watts (W).
energy: The ability to cause change or do work; appears in many forms such as kinetic, potential, thermal, and chemical.
pulley: A wheel with a groove for a rope or cable that can change the direction of a force and, in systems, provide mechanical advantage.
watt (W): The SI unit of power; one watt equals one joule per second.
joule (J): The SI unit of work and energy; one joule is one newton of force acting over one meter of distance.
inclined plane: A sloping surface (ramp) that allows a load to be raised with less force over a longer distance.
kinetic energy: Energy associated with the motion of an object.
simple machine: A basic mechanical device, such as a lever, pulley, or inclined plane, that changes the magnitude or direction of a force.
thermal energy: The total random kinetic energy of particles in a substance; related to temperature.
chemical energy: Energy stored in the bonds of chemical compounds, such as food, fuels, and batteries.
mechanical advantage: The factor by which a machine multiplies the input force, often expressed as output force divided by input force.
elastic potential energy: Energy stored when an object is stretched or compressed, such as a spring or rubber band.
law of conservation of energy: Principle stating that energy cannot be created or destroyed, only transferred or transformed; total energy remains constant.
gravitational potential energy: Energy stored in an object due to its height in a gravitational field.