Hsc Physics Notes - Space
Physics Stage 6 – Yr 12 Notes
9.2 Space:
Context 1 – The Earth has a gravitational field that exerts a force on objects both on it and around it.
Define weight as the force on an object due to a gravitational field
Mass (m): • The amount of matter in a body • Constant anywhere in the universe • Scalar quantity • Measured in Kilograms (Kg)
Weight (W): • The force acting on an object due to a gravitational field • Attractive force • Vector quantity • Direction – following a line between the centre of masses • Measured in Newtons (N) • According to Newtons 2nd Law – F = ma: Weight = Mass x Acceleration due to gravity (W = mg) • Gravitational Force of Attraction between 2 bodies: F = Gm1m2 r2 • Note: Universal constant of gravitation = 6.67 x 10-11 Nm2kg-2
Explain that a change in gravitational potential energy is related to work done
Work done is the measure of how much energy was used to displace an object a specified distance (W = Fs). When an object is moved away from the origin of a gravitational field it gains gravitational potential energy which is the work done.
W = Fs = ∆KE = -∆Ep
Define gravitational potential energy as the work done to move an object from a very large distance away to a point in a gravitational field
EP = - G m1m2 r
Gravitational potential energy is the work done to move an object from a very large distance (ie. infinity) to a point in a gravitational field. Zero gravitational energy is defined as a point in infinity where the gravitational effects of all mass, would be zero. GPE is negative as the system loses energy when trying to remain at a point in a gravitational field. However, as seen from the diagram the further from the earth the less GPE required.
Example:
If a 1kg stone was raised 100m the work done would be 980J, however this is now GPE and will be converted to 980J
9.2 Space:
Context 1 – The Earth has a gravitational field that exerts a force on objects both on it and around it.
Define weight as the force on an object due to a gravitational field
Mass (m): • The amount of matter in a body • Constant anywhere in the universe • Scalar quantity • Measured in Kilograms (Kg)
Weight (W): • The force acting on an object due to a gravitational field • Attractive force • Vector quantity • Direction – following a line between the centre of masses • Measured in Newtons (N) • According to Newtons 2nd Law – F = ma: Weight = Mass x Acceleration due to gravity (W = mg) • Gravitational Force of Attraction between 2 bodies: F = Gm1m2 r2 • Note: Universal constant of gravitation = 6.67 x 10-11 Nm2kg-2
Explain that a change in gravitational potential energy is related to work done
Work done is the measure of how much energy was used to displace an object a specified distance (W = Fs). When an object is moved away from the origin of a gravitational field it gains gravitational potential energy which is the work done.
W = Fs = ∆KE = -∆Ep
Define gravitational potential energy as the work done to move an object from a very large distance away to a point in a gravitational field
EP = - G m1m2 r
Gravitational potential energy is the work done to move an object from a very large distance (ie. infinity) to a point in a gravitational field. Zero gravitational energy is defined as a point in infinity where the gravitational effects of all mass, would be zero. GPE is negative as the system loses energy when trying to remain at a point in a gravitational field. However, as seen from the diagram the further from the earth the less GPE required.
Example:
If a 1kg stone was raised 100m the work done would be 980J, however this is now GPE and will be converted to 980J