Class Notes (1,100,000)

CA (650,000)

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Astronomy (100)

ASTA01H3 (100)

Parandis Tajbakhsh (10)

Lecture 1

Department

AstronomyCourse Code

ASTA01H3Professor

Parandis TajbakhshLecture

1This

**preview**shows half of the first page. to view the full**3 pages of the document.**Kepler’s 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.

Kepler’s 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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