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PHYSICS: CHAPTER 2 .3 NOTE PACKET
2.3: Newton’s First and Second Laws
I.
Vocabulary: Define the following terms from Chapter 2.3.
a. Inertia-tendency of an object to resist a change in motion.
Chapter 2.3: Newton’s First and Second Laws
II.
Notes:
a. Newton’s First Law of Motion (LAW OF INERTIA)
i. “An object AT REST WILL STAY AT REST, and an object moving at a
constant velocity will CONTINUE MOVING AT A CONSTANT
VELOCITY, unless it is acted upon by an unbalanced force.”
1. If at REST, it stays at REST.
2. If it is MOVING, it continues to MOVE.
a. UNTIL ANOTHER FORCE ACTS UPON IT.
ii. INERTIA
1. “A RESISTANCE TO A CHANGE IN MOTION”
a. Either moving or not.
i. Table cloth pulled from under place setting.
ii. Lurching forward as your car comes to a sudden stop.
2. Directly proportional to the MASS of the object.
a. More mass = MORE force necessary to move or stop it
b. Less mass = LESS force necessary to move or stop it.
b. Newton’s Second Law of Motion (F = m * a)
i. F = m * a
ii. a = F/m
iii. m = F/a
III.
Assessment Questions
1.
What does Newton’s first law of motion state?
An object at rest will remain at rest and an object in motion will stay in motion at a
constant velocity unless it is acted upon by an unbalanced force.
2.
Why is Newton’s first law of motion sometimes called the law of inertia?
It is sometimes referred to as the law of inertia because it describes an objects tendency
to resist changes in motion.
3.
Use what you know about inertia to explain why you feel pressed back into the seat of a
car when it accelerates.
The passengers keep moving until acted upon by the unbalanced force exerted by the
seatbelt.
4.
State Newton’s second law of motion in your own words.
Acceleration depends on the object’s mass and ton the net force acting on the object.
5.
How could you keep an object’s acceleration the same if the force acting on the object
were doubled?
Double the mass.
6.
Using what you know about Newton’s second law, explain why a car with a large mass
might use more fuel than a car with a smaller mass. Assume both cards drive the same
distance.
It would use more force to start or stop the car.
7.
8.
9.
10.
Calculating Force: Find the force it would take to accelerate an 800 kg car at a rate of 5
m/s2. (*Show all work: Set-up, Substitute, Solve)
F= m*a= 800kg* 5m/s2 =4000 N
Calculating Force: What is the net force acting on a .15 kg hockey puck accelerating at a
rate of 12 m/s2. (*Show all work: Set-up, Substitute, Solve)
F= m*a= .15kg* 12m/s2 = 1.8 N
Explain how force, mass and acceleration are related by Newton’s second law of motion.
Acceleration = F/m
F= m*a
m= F/a
A 7.3 kg bowling ball accelerates at a rate of 3.7 m/s2. What is the force acting on the
bowling ball?
F= 7.3kg* 3.7m/s2= 27.01 N