Lecture 1 - Intro and Newton's First Law Flashcards
Why does a motionless skater tend to remain motionless?
A body at rest tends to remain at rest due to the skater’s INTERTIA.
Define Inertia.
The tendency of objects in motion to stay in motion and the objects at rest to stay in rest. It is proportional to an objects mass (bigger mass = )
What two properties depend on the number of atoms in the object?
Inertia and Mass. The more electrons, protons, and neutrons = the greater the mass (and inertia).
What is the average atomic weight of a human approximately equal to?
5.9 grams/mole.
Why does a moving skater tend to continue moving?
A body in motion tends to remain in motion. Observed due to the skater’s inertia.
What is Newton’s First Law?
An object free of external “influences” moves (or is subject to zero net force) in a straight line and covers equal distances in equal times - AKA a constant velocity.
What is the special case to Newton’s First Law?
A motionless object obeys this law as a special case because it has ZERO movement. It is “moving” at a constant velocity of zero.
How can we describe the motion of a coasting skater?
The skater moves at a constant speed in a constant direction.
Define force.
A push or pull.
Define Position.
An object’s location. It is a distance (magnitude/scalar) and a direction from a reference - therefore it is a vector quantity.
Define Velocity.
Its change in position with time (RATE of change in position). It is speed (magnitude/scalar) and direction of motion, relative to a reference - therefore it is a vector quantity.
Name all the vector quantities:
Position, velocity, force, acceleration,
What is a vector quantity?
A quantity that has both magnitude (or a scalar quantity) and direction.
Distance and speed are —- quanitities.
Scalar.
True or False: a coasting skater moves at a constant velocity.
True. Key word: coasting.
Why is force a vector quantity?
Because it is the amount and direction of the push or pull. The net force is the vector sum of all forces on an object.
How does a skater start, stop, or turn?
A non-zero net force causes the skater to accelerate.
Define acceleration.
Change in velocity with time. It is the RATE of change in velocity so it is a vector quantity.
What is Newton’s Second Law?
An object’s acceleration is equal to the net force exerted on it divided by its mass and that acceleration is in the same direction as the net force.
What is the equation for acceleration?
Acceleration = net force / mass
(effect) (cause) (resistance to cause)
What is the equation for (net) force?
Force = mass x acceleration (f=ma)
What are units for:
position
velocity
acceleration
force
mass
m
m/s
m/s^2
N (newtons)
kg
Why does a skater need ice or wheels to skate?
Real-world complications such as friction, gravity, etc. usually mask inertia.
What conditions are needed to observe inertia?
Work on level ground (to minimize gravity’s effects) and use wheels, ice or air support (minimize friction).
What happens when you experience no external forces?
- you coast; move at a constant velocity
- when at rest, you remain at rest
- when moving, you move steadily and straight
What happens when you experience external forces?
- you accelerate; move at a CHANGING velocity
- acceleration depends on force and mass
- greater force = greater acceleration
- greater mass = smaller acceleration
