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Astronomy – Book Notes
4.1 Describing Motion: Examples from Daily Life

Speed, Velocity, and Acceleration

Speed:
The rate at which an object moves.
Its units are distance divided by time, such as m/s or
km/hr.
o
Says how far something will go in a certain amount of time
o
Ex: 100 km/hr (60mi/ hr)

Velocity:
o
Tells us both speed and direction
o
Ex: 100 km/hr due north

Acceleration:
The rate at which an object’s velocity changes.
Its standard units are m/s squared.
o
Tells if its velocity is changing in any way (in speed, direction, or both)
o
Slowing down or turning is also accelerating
o
Slowing down = negative acceleration

The Acceleration of Gravity

Objects accelerate as they fall

Gravity accelerates all objects by the same amount, regardless of their mass.

Acceleration of gravity:
The acceleration of a falling object.
On Earth, the acceleration of
gravity, designated by
g
, is 9.8 m/s squared.
o
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 Spring '08
 HORNSTEIN
 Astronomy

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