Unit Four: Energy- essential knowledge

What is a system and how are they treated?

A system is an object or a collection of objects that are treated as having no internal structure.

What quantities are conserved in all systems under all circumstances?

Energy, charge, linear momentum, and angular momentum are conserved in all systems under all circumstances.

What is the difference between a closed (or isolated) system and an open system?

In a closed system, conserved quantities remain constant and do not exchange with the surroundings. In an open system, conserved quantities can be exchanged with the surroundings.

What is an interaction in the context of a physical system?

An interaction can be a force exerted by objects outside the system or the transfer of a conserved quantity with objects outside the system.

How is the boundary between a system and its environment determined?

The placement of the boundary is a decision made by the person analyzing the situation to simplify or assist in the analysis.

How does the component of the net force parallel or antiparallel to an object's displacement affect its kinetic energy?

The parallel component of the net force will increase the object's kinetic energy, while the antiparallel component will decrease it.

How does the component of the net force perpendicular to an object's displacement affect its motion?

The perpendicular component of the net force can change the direction of the object's motion without changing its kinetic energy. This applies to uniform circular motion and projectile motion.

Can a rotating rigid body be considered a system, and what types of kinetic energy can it have?

Yes, a rotating rigid body can be considered a system and may have both translational and rotational kinetic energy.

What is internal energy in a system with an internal structure?

Internal energy is the energy associated with changes in a system's internal structure. Changes in internal structure can result in changes in internal energy.

What is the difference between work and potential energy in terms of forces acting on a system?

Work describes forces external to the system, while potential energy is associated with internal interactions between parts of the system.

How does the path taken by an object affect the work done by a conservative force?

The work done by a conservative force is independent of the path taken by the object.

What happens to potential energy when there is a change in a system's internal structure?

Changes in the internal structure can result in changes in potential energy, such as in mass-spring oscillators or objects falling in a gravitational field.

How does a change in a system's potential energy affect its kinetic energy in a closed system?

Since energy is constant in a closed system, a change in potential energy can result in an opposite change in kinetic energy.

How might the construction of a system constrain changes in potential and kinetic energy?

The specific construction of a system can impose constraints on how potential and kinetic energies change, limiting the types or magnitudes of energy transformations.