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Lecture 4

# Astronomy 1021 Lecture Notes - Lecture 4: Circular Motion, List Of Association Football Teams To Have Won Four Or More Trophies In One Season, Net Force

by OC2541519

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**preview**shows page 1. to view the full**4 pages of the document.**Astronomy – Chapter 4

Scalars and Vectors

- Scalar (number); distance, speed

- Vector (number and direction); Displacement, velocity, acceleration

Speed

- Tells us how far in a certain time (100km/hr)

Velocity

- Requires speed and direction (100km/hr eastward)

Acceleration

- Change in velocity in a certain time (change is speed, direction, or both)

- Speeding up

- Slowing down (deceleration)

- Changing direction

- Units: meters per sec per sec (m/s2) e.g., 0 to 100 km/h in 4 seconds

- Can feel acceleration (e.g., train or plane), whereas you don’t feel constant speed

Examples

- Falling apple; changed speed (it gets faster as it falls), same direction (always falls

down), Falling objects accelerate due to gravity

- Ball on string; Same speed (in uniform circular motion), Changed direction (swings

around in circle)

Acceleration Due to Gravity

- At the Earth’s surface: g ≈ 10 m/s2 – An object is initially stationary. We then drop it.

After 1 second, the object will be moving with a speed of 10 m/s, after 2 seconds it will

be moving at 20 m/s, and so on, until it hits the ground

- At the Moon’s surface: g ≈ 1.7 m/s2

Mass

- Amount of matter in an object

- Measured kilograms (international

system)

- On Earth, we often think about this in

terms of an objects weight but this is

not correct; mass and weight are

different (but related) things

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