Physics U16 and U17 Important

Angular Velocity, w: When an object moves in a circular path at a rate of change of angle travelled.

Centripetal acceleration, a: When an object moves in a circular path, the centripetal acceleration is perpendicular to the tangent velocity.

A binary Star System consists of 2 stars orbiting around each other. The centripetal force on 2 stars is provided by the gravitational force between the 2 stars.

The line of gravitational force is the direction of the force acting on a unit mass.

Point Mass: All field lines appear to be produced from the same point, and are radial.

The force of gravity acts directly proportional to the product of 2 masses and inversely proportional to the separation squared, provided that the masses are point masses.

Radian: When the subtended length is equal to the radius, the angle subtended at the centre of the circle.

Angular Speed: Angular displacement per unit time.

Gravitational potential at a point is defined as the work done per unit mass in bringing the object from infinity to that point.

Centripetal Force: Resultant force on an object towards the centre of a circle, when the object is rotating in a circular path at constant speed.

Gravitational Field: Region in space where a mass experiences a gravitational force.

Gravitational force is the product of 2 masses divided by the square of the separation.

The gravitational field of force is the region where the gravitational force is exerted on a unit mass.

Gravitational field lines denote the direction of the gravitational force on a unit mass.

Gravitational potential is work done per unit mass.

• Field lines are radial.
• Parallel
• So appear equidistant
• g is constant

Q. Explain why, at the surface of the sphere, g has the opposite sign to R.

Ans: Gravitational force is attractive, so it points to the centre. Hence, force is in the opposite direction to displacement.