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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


Department
Astronomy
Course Code
ASTR 1021
Professor
Robert Cockcroft
Lecture
4

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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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