VCE Physics - Summary Sheet
Movement
ANALYSING MOVEMENT
1. Describing motion
Scalar quantities - have size (or magnitude) but not direction.
Vecor quantities - have both magnitude and direction.
Š An even curve describes a changing velocity (but a constant acceleration). The average velocity is found by the gradient over an interval.
The instantaneous velocity is found by the gradient of a tangent to the
curve.
Velocity vs time graphs
Distance is a scalar quantity.
Displacement is a vector quantity and measures change in position.
Speed is a scalar quantity that measures the rate at which distance is
changing over time.
formula
Velocity is a vector quantity that measures the rate at which displacement
is changing over time.
formula
or
Acceleration is a vector quantity that measures the rate at which velocity
is changing with time.
Š Displacement is given by the area under the graph (or by using the
formula for average velocity given above).
Š Acceleration is given by the gradient of the graph. (find the gradient
over an interval for average acceleration or the gradient of a tangent for
instantaneous acceleration)
Acceleration vs time graphs
Notes
Š Change in velocity is given by the area under the graph. (To find the
actual velocity we need to know the initial velocity)
Notes
2. Graphing motion
Position vs time graphs
Š A straight line describes a constant velocity (zero acceleration). This
velocity is given by the gradient of the line.
VCE Physics - Summary Sheet
Movement
The supporting force that opposes gravity is called the normal reaction
force. This always acts at a 90 degree angle to the surface).
3. Equations of motion
The bulk movement of an object is the overall movement not including
other motion such as spinning.
Notes
formula
formula
Notes
2. Newton’s first law
This is sometimes called the law of inertia. (Inertia is the tendency of an
object to resist a change in its motion.
Every object continues in its state of rest or motion unless made to change by
law
a non-zero net force.
Forces acting on a car driving on a horizontal road...
FORCES IN ACTION
1. Introducing forces
Note: if the vector sum of these forces is zero (a zero net force) then the car will
maintain a constant velocity.
Š A Force describes a push or a pull
Š Force is a vector quantity. The S.I. unit is the Newton (N)
Notes
Gravity
Mass (m) describes the amount of matter in an object and all objects that
have mass exert a gravitational pull. The force on an object due to gravity
is called Weight (W).
formula
Where g is gravitational field strength. On Earth g = 9.81 N kg-1
Friction
Friction is a resistance force formed when one object moves against another
Fluid friction is the friction formed by objects moving through air and water.
Net force
The net force is the vector sum of the forces acting on an object (Remember
that to add vectors they must be arranged head to tail).
VCE Physics - Summary Sheet
Movement
3. Newton’s second law
Notes
As the net force on an object increases so does the acceleration of the object.
Law
The rate of acceleration depends on the mass of the object.
formula
Real situations involve many different forces making it hard to calculate the
net force without using idealisations which assume that some values are
negligible (so small that they can be ignored).
Falling Objects
Š Falling objects are subject to two forces, weight and air resistance.
Š If the air resistance is negligible then the acceleration of a falling object
depends only on the gravitational field strength.
Š If air resistance is not negligible then the acceleration will be less if the
mass is more, as described by this formula...
a
formula
where A is air resistance
Multiple bodies
Problems involving multiple bodies can be simplified by treating the bodies
as one object and considering only the forces acting on the whole system.
MECHANICAL INTERACTIONS
1. Collisions
Notes
The law of conservation of momentum states that...
If there are no external forces acting on a system then the total momentum
law
remains constant.
In order for there to be no external forces acting on a system the following
idealisations must be used...
Š The driving forces must be zero
Š The friction forces (including air resistance) must be zero
Under these conditions we can use the momentum to observe a system
before and after a collision.
Notes
4. Newton’s third law
For every action there is an equal
and opposite reaction
law
This describes how forward motion occurs...
1. An object pushes back on an object with a much greater inertia.
2. A reaction force pushes back on the first object propelling it forwards.
5. Momentum
Momentum describes how much force is required to stop a moving object.
Momentum (p) is a vector quantity with unit kg m s-1 and is found by...
Impulse (I) is the change in momentum it is a vector quantity with unit N s.
Here are several ways of finding impulse...
I = pf - pi = ∆p =
Impulse can also be found by the area under a force vs time graph.
VCE Physics - Summary Sheet
Movement
Elastic potential energy is the energy stored in an object as a result of a
reversible change in shape.
2. Mechanical Energy
Energy is the capacity to do work. It is a scalar quantity with unit Joule (J)
where 1J = 1N × 1m.
Work (W) is done when energy is transferred to or from an object by the
action of a force.
formula
If the displacement does not occur in the same direction of the force, we
can calculate the work by using trigonometry to find the component of the
displacement vector that operates in the same direction as the force.
formula
Elastic potential energy can also be found by the area under a force vs
displacement graph.
Conservation of total mechanical energy
When energy is transformed between different types of mechanical energy
some is usually lost to the environment (for example as heat or sound). If air
resistance and other types of friction are small then this energy loss will be
negligible. Under these conditions the total amount of mechanical energy
will be conserved.
Notes
here W = F x cos θ
Work is mechanical energy. There are three main types of mechanical energy. Kinetic energy, gravitational potential energy and elastic potential
energy.
Notes
3. Power
Power is the rate at which energy is transferred or transformed. It has the
symbol P and the unit Watt (W) where 1W = 1Js-1.
and
Notes
Kinetic Energy
Kinetic energy is the energy associated with the movement of an object.
Kinetic energy depends on mass and speed as follows...
and
Potential Energy
Potential energy is energy that is stored.
Gravitational potential energy is the energy stored in an object as a result
of its elevated position while under the pull of gravity.
P