Potential Energy in Systems

Potential Energy in Systems

How is energy stored?

Vocabulary

Gravitational potential energy: potential energy stored in a system of objects interacting due to
gravitational forces

Electric potential energy: potential energy stored in a system of objects interacting by electric
forces

Magnetic potential energy: potential energy stored in a system of objects interacting by
magnetic forces

Elastic potential energy: potential energy resulting from elastic forces; elastic potential energy is a
combination of different types of energy

Chemical potential energy: potential energy stored in chemical bonds that hold particles of
matter together; chemical potential energy is a combination of different types of energy

1. Gravitational Potential Energy

A system has potential energy if the objects in it have attractive forces
between them but have been pulled apart

Gravitational potential energy: potential energy stored in a system of
objects interacting due to gravitational forces

●A book on a bookshelf, Earth, and the gravitational forces pulling them
together has gravitational potential energy

Depends on the mass of the interacting objects and the space between
them

●Larger book has more potential energy, books closer to the ground
have less potential energy, etc.

1. Gravitational Potential Energy

Gravitational Potential Energy and Mass

The greater the mass, the greater the gravitational potential energy; the
smaller the mass, the less gravitational potential energy

Gravitational Potential Energy and Distance

The further the distance from the gravitational pole, the more gravitational
potential energy; the closer the distance from the gravitational pole, the
less gravitational potential energy

Open Ended

Explain gravitational energy and the two things it depends on

Electric Potential Energy

Electric forces are involved in storing electric potential energy

Electric potential energy: potential energy stored in a system of objects
interacting by electric forces

Depends on three factors: the amount of charge on the objects in the
system, the signs of the charges in the system, and the distance between
the objects in the system

2. Electric Potential Energy

Electric Potential Energy and Amount of Net Charge

No charge → no electric potential energy; some charge → some electric
potential energy; more charge → more electric potential

Electric Potential Energy and the Signs of Charges

Same signs → repulsive; different signs → attractive

Electric Potential Energy and the Distance Between Objects

Close repulsive forces → large electric potential energy; Far repulsive forces
→ small electric potential energy; close attractive forces → small electric
potential energy; far attractive forces → large electric forces

Open Ended

What factors determine the amount of electric potential energy

3. Magnetic Potential Energy

Magnetic potential energy: potential energy stored in a system of objects
interacting by magnetic forces

Depends on three factors: strength of magnets, orientation of magnets,
and distance between the magnets

Repelling magnets close together → more magnetic potential energy;
repelling magnets further apart → less magnetic potential energy;
attracting magnets close together → less magnetic potential energy;
attracting magnets further apart → more magnetic potential energy

Open Ended

What factors determine the amount of magnetic potential energy?

4. Other Types of Potential Energy

Elastic potential energy: potential energy resulting from elastic forces; elastic
potential energy is a combination of different types of energy

●Combination of kinetic energy, electric potential energy, and magnetic
potential energy

●Things that “bounce back”

○Stress balls, springs, rubber bands

Chemical potential energy: potential energy stored in chemical bonds that hold
particles of matter together; chemical potential energy is a combination of
different types of energy

●Combination of kinetic energy, electric potential energy, and magnetic
potential energy

●Bonds holding matter together are broken

○Batteries, gasoline

Open Ended

What are the three kinds of energy that combine to make elastic potential energy and chemical potential energy?

5. Evaluating Bridge Design

Bridge needs to be built to connect two sides of a city that is separated by a river

Criteria: must be movable to allow tall ships to pass through, must look good

Constraints: can’t go over budget, not interfere with nearby businesses

Swing Bridge → doesn’t interfere with the ocean view, but the pole in the center
might make it difficult for some ships to pass through, docks will have to be torn
down to accommodate

Lift Bridge → doesn’t require docks to be torn down, low energy usage, tall ships
won’t be able to pass through

Bascule Bridge → doesn’t interfere with property around bridge, saves energy,
opens the river to ships of any size

Open Ended

List the criteria and constraints for the bridge project:

Multiple Choice

Which bridge design is best based on the criteria and constraints?

• Swing bridge

• Bascule bridge

• Lift bridge