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ASTA01H3 (100)
Lecture 1

ASTA01H3 Lecture Notes - Lecture 1: Critical Role, Planetary System, Net Force


Department
Astronomy
Course Code
ASTA01H3
Professor
Parandis Tajbakhsh
Lecture
1

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Keplers Second Law: As the planet moves around its orbit, it sweeps out equal areas in
equal times. This in turn means that the planet moves a greater distance on the orbit when
in perihelion contrary to when it is at aphelion.
This law also implies that planet has its biggest orbital velocity at perihelion and smallest
orbital velocity at aphelion.
Keplers Third Law: More distant planets orbit the Sun at slower average speeds,
obeying the precise mathematical relationship: P2yr = a3AU
Newton’s Laws of Motion
The entire history and evolution of universe is the result of the interaction between matter
and energy. These interactions can be described by a number of laws, first expounded by
Isaac Newton.
Newton devised three laws that are obeyed by all moving bodies. These are known as
Newton’s Laws of Motion.
Velocity: Total distance moved divided by time. It also has the direction of movement built
within it.
Acceleration: Rate of change of velocity with time. Acceleration could be negative or
positive. Deceleration is an example of negative acceleration. Change of direction is also
an example of acceleration (recall that velocity has speed and direction built into it).
First Law: A body will remain at rest or continue in a uniform motion on a straight line if the
net force acting on the body is zero.
Example: When a car is moving at constant velocity, then the forces exerted by the wheels
to drive the car forward is equal to the opposing forces such as friction and wind
resistance.
Newton’s first law is a statement about inertia. Inertia is defined as the resistance of an
object to any change in its state of motion.
Second Law: The rate of change of speed (acceleration) of a body is directly proportional
to the force exerted on it and inversely proportional to its mass.
The second law states: Force = Mass Acceleration. This interprets to the fact that the
more massive an object is the more force is required to change the speed of that object.
The mass of an object is defined as the amount of matter that exist in that object.
Unit of measurement of Force is Newton!
Example: It is easier to push an empty shopping cart than when it is full. In both cases, you
exert the same amount of force, but the change in speed of an empty shopping cart is
much bigger than a full shopping cart. The difference comes form the difference between
the masses.
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