PHY C4: Energy Stores & Transfers

What is Energy?

The capacity to do work.

What is the SI unit for Energy?

Joule (J).

How is energy present in a system?

In different stores, and systems can transfer energy from one store to another.

What are the eight types of Energy Stores?

Kinetic energy, Gravitational potential energy, Chemical potential energy, Nuclear energy, Elastic potential energy, Internal energy, Magnetic potential energy (not in H1/H2 syllabus), Electric potential energy.

What is Kinetic Energy?

Energy due to the motion of an object.

What is Gravitational Potential Energy?

Energy due to the position of a mass in an external gravitational field.

What is Chemical Potential Energy?

Energy due to the structural arrangement of atoms/molecules in a substance.

What is Electric Potential Energy?

Energy due to the position of a charge in an external electric field.

What is Magnetic Potential Energy? (Not in H1/H2 Syllabus)

Energy due to the orientation of a magnetic dipole to an external magnetic field.

What is Nuclear Energy?

Energy stored in atomic nuclei – released during fusion or fission processes.

What is Elastic Potential Energy?

Energy due to the physical deformation of an object (e.g., compressing or stretching a spring).

What is Internal Energy?

Consists of two components: energy due to the random motion of atoms/molecules (internal kinetic energy) and energy due to interatomic/intermolecular forces (internal potential energy).

What are the four pathways for Energy Transfer?

Mechanical (work done), Electrical (electric current), Heating (temperature difference), Wave propagation (mechanical/electromagnetic waves).

What is Work Done (W) by a constant force?

In scientific terms, work is done by a force on an object when the object is moved in the direction of the force.

What is the formula for Work Done by a constant force F?

W = (F cosθ)s = Fs cosθ, where Fcosθ is the component of force in the direction of displacement.

What is the SI unit for Work Done?

Joule (J).

What is a Joule (J)?

1 J is the work done on an object by a force of 1 N when the object is displaced by 1 m in the direction of the force.

What does Positive Work Done mean?

The component of force is in the same direction as displacement (cosθ > 0) -> increases system energy.

What does Negative Work Done mean?

The component of force is in the opposite direction to displacement (cosθ < 0) -> decreases system energy.

What happens if the force component is perpendicular to displacement?

No work is done by that component.

What is Work Done by a variable force?

Can be determined by finding the area under the force – displacement graph.

What is the relationship between Work Done by a field and change in Potential Energy?

The work done W by the field in moving the object is equal to the negative of the change in its potential energy U (W = -ΔU).

What is the relationship between Force and Potential Energy Gradient?

The magnitude of the force is equal to the potential energy gradient, and acts in the direction of decreasing potential energy (F = -dU/ds).