# Newtons 2nd and 3rd Law

Document Sample

```					Newton’s   2 nd   and   3rd   Law
A. Newton’s 2nd Law
B. Newton’s 3rd Law
C. Project
A. Newton’s 2nd Law

 The acceleration of an object is dependent upon
two variables:
– Fnet acting on the object
– Mass of the object
 The acceleration of an object depends directly
upon the net force acting upon the object and
inversely upon the mass of the object
 As Fnet increases, acceleration increased
 As mass increases, acceleration decreases
A. Newton’s 2nd Law
A. Newton’s 2nd Law

 The net force is equal to the product of the
object's mass and its acceleration.
– Fnet = ma

 Acceleration is in the same direction as Fnet
 Remember: the net force is the vector sum
of all the forces
A. Newton’s 2nd Law

 What acceleration will result when a 12-N
net force is applied to a 3-kg object? A 6-kg
object?

 A net force of 16 N causes a mass to
accelerate at the rate of 5 m/s2. Determine
the mass.
A. Newton’s 2nd Law

Net Force
• Fnet = ma
Gravitational Force
• Fgrav = mg
Frictional Force
• Ffrict = μ(Fnorm)
A. Newton’s 2nd Law
 An applied force of 50 N is used to accelerate an
object to the right across a frictional surface. The
object encounters 10 N of friction. Use the diagram
to determine the normal force, the net force, the
mass, and the acceleration of the object. (Neglect air
resistance.)
A. Newton’s 2nd Law
 An applied force of 50 N is used to accelerate an object to
the right across a frictional surface. The object encounters 10
N of friction. Use the diagram to determine the normal force,
the net force, the mass, and the acceleration of the object.
(Neglect air resistance.)

Fnorm = 80 N
m = 8 kg
a = 5 m/s2
Fnet = 40 N,
right
A. Newton’s 2nd Law
 An applied force of 20 N is used to accelerate an object
to the right across a frictional surface. The object
encounters 10 N of friction. Use the diagram to
determine the normal force, the net force, the
coefficient of friction (µ) between the object and the
surface, the mass, and the acceleration of the object.
(Neglect air resistance.)
A. Newton’s 2nd Law
 An applied force of 20 N is used to accelerate an object
to the right across a frictional surface. The object
encounters 10 N of friction. Use the diagram to
determine the normal force, the net force, the
coefficient of friction (µ) between the object and the
surface, the mass, and the acceleration of the object.
(Neglect air resistance.)

Fnorm = 100N
μ = 0.1
m = 10 kg
a = 1 m/s2 right
Fnet = 10N right
A. Newton’s 2nd Law
 A 5-kg object is sliding to the right and encountering a
friction force which slows it down. The coefficient of
friction (µ) between the object and the surface is 0.1.
Determine the force of gravity, the normal force, the force
of friction, the net force, and the acceleration. (Neglect air
resistance.)
A. Newton’s 2nd Law
 A 5-kg object is sliding to the right and encountering a
friction force which slows it down. The coefficient of
friction (µ) between the object and the surface is 0.1.
Determine the force of gravity, the normal force, the force
of friction, the net force, and the acceleration. (Neglect air
resistance.)

Fnorm = 50N
Ffrict = 5N
Fgrav = 50N
m = 5kg
a = 1 m/s2
Fnet = 5N left
B. Newton’s 3rd Law

Whenever one object exerts a force on
a second object, the second object
exerts an equal and opposite force on
the first.

Action-reaction pairs never act on
same object.
B. Newton’s 3rd Law

 Two objects define a system for a Newton’s
third law interaction.
 We are not considering (necessarily) the net
force acting on an object.
 An object cannot exert a force on itself to
cause an acceleration.
Newton’s 3rd Law
Action and Reaction on Different Masses

Consider you and the earth

Action: earth pulls on you

Reaction: you pull on earth
B. Newton’s 3rd Law

Reaction: road pushes on tire   Action: tire pushes on road
B. Newton’s 3rd Law

Reaction: gases push on rocket

Action: rocket pushes on gases
B. Newton’s 3rd Law
A bug and a car collide. Which experiences
the greater force?
(a) bug
(b) car
(c) neither, they both experience the same
magnitude of force
B. Newton’s 3rd Law
Consider hitting a baseball with a bat. If we
call the force applied to the ball by the bat the
action force, identify the reaction force.

(a) the force applied to the bat by the hands
(b) the force applied to the bat by the ball
(c) the force the ball carries with it in flight
(d) the centrifugal force in the swing
C. Project: Balloon Rocket
Racer
 Design a small car powered by a balloon
and explain how the third law of motion
describes its propulsion

DUE:

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 0 posted: 7/2/2013 language: English pages: 20
How are you planning on using Docstoc?