Topic 10 - Fields

Gravitational Potential Energy (unit: J)

The work done on a small mass in bringing it from infinity to a point in the gravitational field.

Gravitational Potential (unit: Jkg-1)

The work done per unit mass on a small mass in bringing it in from infinity to a point in the gravitational field.

Electric Field Strength (unit: NC-1)

The force per unit charge on a small positive charge at a point in the electric field.

Electric Potential Energy (unit: J)

The work done on a small positive test charge in bringing it in from infinity to a point in the electric field.

Electric Potential (unit: JC-1)

The work done per unit charge on a small positive test charge in bringing it in from infinity to a point in the electric field.

Why is gravitational potential negative?

• Potential is defined to be zero at infinity

• Positive amount of work needs to be supplied for a mass to reach infinity

Subsequent motion of projectile after fired upwards

• Velocity decreases

• Magnitude of deceleration decreases

• Velocity becomes constant

Orbital speed decrease, what effects?

• KE will initially decrease → TE decrease

• Earth moves closer to Sun

• New orbit with greater speed

• Change ellipticity of orbit