Lecture 1 - Intro and Newton's First Law

Question 1

Why does a motionless skater tend to remain motionless?

Answer 1

A body at rest tends to remain at rest due to the skater’s INTERTIA.

Question 2

Define Inertia.

Answer 2

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 = )

Question 3

What two properties depend on the number of atoms in the object?

Answer 3

Inertia and Mass. The more electrons, protons, and neutrons = the greater the mass (and inertia).

Question 4

What is the average atomic weight of a human approximately equal to?

Answer 4

5.9 grams/mole.

Question 5

Why does a moving skater tend to continue moving?

Answer 5

A body in motion tends to remain in motion. Observed due to the skater’s inertia.

Question 6

What is Newton’s First Law?

Answer 6

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.

Question 7

What is the special case to Newton’s First Law?

Answer 7

A motionless object obeys this law as a special case because it has ZERO movement. It is “moving” at a constant velocity of zero.

Question 8

How can we describe the motion of a coasting skater?

Answer 8

The skater moves at a constant speed in a constant direction.

Question 9

Define force.

Answer 9

A push or pull.

Question 10

Define Position.

Answer 10

An object’s location. It is a distance (magnitude/scalar) and a direction from a reference - therefore it is a vector quantity.

Question 11

Define Velocity.

Answer 11

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.

Question 12

Name all the vector quantities:

Answer 12

Position, velocity, force, acceleration,

Question 13

What is a vector quantity?

Answer 13

A quantity that has both magnitude (or a scalar quantity) and direction.

Question 14

Distance and speed are —- quanitities.

Answer 14

Scalar.

Question 15

True or False: a coasting skater moves at a constant velocity.

Answer 15

True. Key word: coasting.

Question 16

Why is force a vector quantity?

Answer 16

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.

Question 17

How does a skater start, stop, or turn?

Answer 17

A non-zero net force causes the skater to accelerate.

Question 18

Define acceleration.

Answer 18

Change in velocity with time. It is the RATE of change in velocity so it is a vector quantity.

Question 19

What is Newton’s Second Law?

Answer 19

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.

Question 20

What is the equation for acceleration?

Answer 20

Acceleration = net force / mass
(effect) (cause) (resistance to cause)

Question 21

What is the equation for (net) force?

Answer 21

Force = mass x acceleration (f=ma)

Question 22

What are units for:
position
velocity
acceleration
force
mass

Answer 22

m
m/s
m/s^2
N (newtons)
kg

Question 23

Why does a skater need ice or wheels to skate?

Answer 23

Real-world complications such as friction, gravity, etc. usually mask inertia.

Question 24

What conditions are needed to observe inertia?

Answer 24

Work on level ground (to minimize gravity’s effects) and use wheels, ice or air support (minimize friction).

Question 25

What happens when you experience no external forces?

Answer 25

• you coast; move at a constant velocity
• when at rest, you remain at rest
• when moving, you move steadily and straight

Question 26

What happens when you experience external forces?

Answer 26

• you accelerate; move at a CHANGING velocity
• acceleration depends on force and mass
• greater force = greater acceleration
• greater mass = smaller acceleration