Chapter 3 Conceptual Physics

These are literally just the notes from the book. #Hewitt

Are things appearing to be at rest truly at rest?

no, they are just moving relative to the sun and stars

When we discuss the motion of something what are we describing?

the motion relative to something else

Unless stated otherwise, when we discuss the speeds of things in our environment, what do we mean?

relative to the surface of Earth

Who defined speed as the distance covered per unit of time?

Galileo

What are the units of speed?

any combination of distance and time units (examples: km/h, mi/h, m/s)

What is instantaneous speed?

the speed at any instance (example: speed on a speedometer)

How is average speed different than instantaneous speed?

on a car trip (for example), we experience a variety of speeds that aren’t reflected as well in the average speed. Instantaneous speed is the speed at any moment

What is velocity?

when we know the speed and direction of motion for an object

Give an example of speed and an example of velocity

60 km/h (speed)

60 km/h north (velocity)

What Is a vector quantity?

a quantity that specifies direction as well as magnitude (examples: velocity, force)

What is a scalar quantity?

a quantity that requires only magnitude for a description (example: speed)

What does constant speed mean?

steady speed, something that doesn’t speed up or slow down

What does constant velocity mean?

both constant speed and constant direction

What does an object’s path look like if its in constant velocity?

a straight line

If an object has a curved path is it in constant velocity?

no because the direction changes meaning the velocity changes

In which conditions does velocity change?

if either the speed or direction changes (or both change)

What is acceleration?

how quickly and in what direction velocity changes

Is acceleration just the total change in velocity?

no, it is also the time rate of change or change per second in velocity

What does acceleration apply to?

increases as well as decreases in velocity

Applying the breaks is what kind of acceleration?

deceleration

Why do we accelerate whenever we’re moving in a curved path even if we are moving at constant speed?

our direction is changing every instant and therefore our velocity is changing

What can we express acceleration as if the direction doesn’t change?

the rate at which speed changes

What does acceleration encompass?

changes in speed and direction

How did Galileo study accelerated motion?

using inclined planes

What did Galileo find in his inclined plane experiments?

a ball rolling down an inclined plane picks up the same amount of speed in successive seconds (the ball rolls with unchanging/ constant acceleration)

What is the instantaneous speed or velocity of the ball at any given time after being released from rest (in Galileo’s experiment)?

equal to its acceleration multiplied by time

If you know the acceleration and number of seconds it has been accelerating what can you find (Galileo’s ball experiment)?

instantaneous speed or velocity

Which inclines did Galileo find to have a greater acceleration?

steeper inclines

When do all objects fall with the same unchanging acceleration?

when air resistance is small enough to be ignored

What is the acceleration of gravity (rounded)?

10 m/s²

What is free fall?

when a falling object is free of all restraints (no friction- with the air or otherwise) and falls under the influence of gravity alone

In each second of free fall, how much speed does an object gain (aka acceleration)?

10 m/s

What letter is used to represent the acceleration of an object in free fall?

g

Is g always constant (or the same value)?

no, on Earth g varies slightly in different locations and on the moon and different planets it also varies

What is the instantaneous speed of an object that is thrown up’s highest point?

0

After an object is thrown up and starts downward what happens?

it begins to fall downward just as if it had been dropped from rest at that height

When an object is thrown up, at what rate does it slow down?

10 m/s each second (the same acceleration it experiences on the way down)

What sign do downward velocities have?

negative

What did Galileo find in relation to distance?

the distance a uniformly accelerating object travels is proportional to the square of time.

Where does a feather and coin fall at the same rate?

in a vacuum, where there is no air and therefore no air resistance

What objects are not appreciably affected by air resistance?

heavier objects (baseballs and stones for example) at ordinary low speeds

Is velocity a rate?

yes