Physics SAT1 - Motion and Relativity

Horizontal Velocity Component

Remains constant in projectile motion in an vacuum

Vertical Velocity Component

Changes in projectile motion due to gravitational acceleration

45 Degrees

Optimal launch angle from ground in a vacuum

Increasing Launch Speed

Increases projectile range

Drag

The resistance force that acts against the motion of an object in air or a fluid.

Terminal Velocity

The maximum speed a free-falling object reaches when the force of gravity equals the force of drag.

Terminal Velocity Acceleration

0ms^-2

Newton’s 2nd Law Derived

Force is equal to the change in momentum over time

Law of Conservation of Momentum

The total momentum before an interaction is equal to the total momentum after an interaction. (in an isolated system)

LOCOM and Newton’s 3rd Law

During an interaction, both objects experience a force of equal magnitude in opposite directions.

Isolated System

Smooth, horizontal, or frictionless

Multi-Image Diagrams

Photos of the motion of an object at regular time intervals

Analysing Multi-Image

Consider all masses, draw vector arrows for initial and final momentums, projectile initial momentum, project final momentum, consider if they are equal.

Spacecraft Propulsion

Ejected gas/ionised particles gain momentum in one direction while the spacecraft experiences equal momentum in the opposite direction, based on LOCOM.

Absorbing Solar Sails

Capture photons of light on black solar sail to gain momentum and acceleration. (Momentum of photon from p to 0)

Reflecting Solar Sails

Reflect photons of light on white solar sail to gain greater momentum and acceleration. (Momentum of photon from p to -p)

Uniform Circular Motion

Motion in a circular path at a constant speed

Velocity in Circular Motion

The velocity at any point is the tangent to the circular path

Centripetal Acceleration

The acceleration experienced by an object undergoing uniform circular motion always acts perpendicularly to the object’s velocity towards the centre of the circular path.

Centripetal Forces

The forces that cause centripetal acceleration

Tension Force

Centripetal force of a string

Friction Force

Centripetal force caused by circular motion, i.e. vehicles turning

Gravitational Force

Centripetal force between one satellite orbiting a larger mass

Normal Force

Centripetal force caused by centrifuge-type motion

Banked Curves

The horizontal component of normal force provides the centripetal force, reducing the friction force necessary.

Newton’s Law of Gravitation

The force between 2 masses is directly proportional to each of their masses and inversely proportional to the distance between them squared.

Direction of Gravitational Force

Acts along the line joining the centre of each mass.

Gravitational Force of >2 Masses

As per the principle of superposition, the force on any of the masses is the vector sum of the gravitational forces due to each mass present.

Gravitational Fields

A mass M has a region of space where all other masses experience the force of gravity

Gravitational Field Notation

Arrows indicate the direction of the field and line density represents the magnitude of the field

Gravitational Field Strength

The force per unit mass at a particular point in the field

Stable Satellite Orbits

Must be circular and have centre of orbit coincide with centre of Earth

Geostationary Satellites

Remains in a fixed position above Earth

Geostationary Conditions

Travels in same orbit direction as Earth, period of 24h, must be equatorial, approx. 36,000km above Earth

Geostationary Satellite Uses

Communication and constant monitoring on a fixed location, but with low resolution

Polar Satellites

Orbits the poles

Polar Conditions

No specific conditions

Polar Satellite Uses

Surveillance and meteorology with higher resolution

Kepler’s Law of Ellipses

All planets move in elliptical orbits with the sun at one focus.

Kepler’s Second Law

A line drawn from the Sun to a planet sweeps out equal areas in equal time intervals.

Kepler’s Third Law

For circular orbits, T²= (4π²r³)/GM