Transcript Chapter 7 Force ppt

Section 1: The Nature of
Force
Force – a push or pull on an object;
causes an object to accelerate.
3 m/s
0 m/s
• Like velocity and acceleration, a force is
described by its strength and by the
direction in which it acts.
• Arrows are used to
show the direction
of the force. The length
of the arrow shows the
strength of the force.
Calculating Force
Force = (mass)(acceleration)
F = ma
measured in units of:
kilogram-meter/second squared
(kgm/s2)
kilogram-meter/second squared
a.k.a.
Newton
(N)
Two Types of Forces
balanced forces – forces of equal strength &
acting in opposite directions; net force
always equals zero Newtons.
5N
5N
Net force = 0 N
unbalanced forces – forces of unequal
strength &/or act in different directions;
causes an object to move.
5N
Net force =
3N
3N
2N
Unbalanced Forces
5N
8N
3N
~7 N
5N
5N
Section 2: Friction & Gravity
friction- the force that two surfaces exert on
each other when they rub against each
other.
4 Types of Friction: (strongest to weakest)
1)
2)
3)
4)
Static – between objects that aren’t moving (ex. Trying
to push a couch)
Sliding – when two objects slide over each other (ex.
Penguin sliding down hill)
Rolling – when object rolls across a surface (ex. Pushing
a bike down the road)
Fluid – materials that flow easily (ex. Air and water)
**List 2 examples of each.
gravity – a force that pulls objects
toward each other.
Gravity causes objects
to accelerate toward
earth at:
9.8 m/s2.
Gravity also causes:
Law of Universal Gravitation
states that due to gravity every object in the
universe is attracted to every other object
in the universe.
Weight
weight is the gravitational pull on an object.
weight = (mass)(gravity)
w = mg
measured in units of:
Kgm/s2 a.k.a. Newtons
Calculate your REAL weight
Step 1) Find your mass:
# of lbs / 2.2 = # of kgs.
Step 2) Calculate your weight
2
w = (# of kgs.)(9.8 m/s )
Gravity in the Solar System
Moon
Venus
Jupiter
Sun
1.2 m/s2
7.98 m/s2
31,000 m/s2
3,244,816.1
m/s2
Newton’s First Law
(Law of Inertia)
Section 3:
An object at rest will remain at
rest, and an object in motion
will remain in motion at a
constant velocity, unless an
unbalanced force acts upon it.
inertia – the tendency of an object to resist
changes in its motion.
Newton’s Second Law
force, mass and acceleration
are related with the formula:
F = ma
50 N
6 m/s2
300 kg
12 m/s2
100 N
300 kg
6 m/s2
100 N
600 kg
Newton’s Third Law
if one object exerts a force on another object,
then the second object will exert a force of
equal strength in the opposite direction back
on the first object.
Fuel
Gas
momentum – the product of an
object’s mass and velocity.
momentum = (mass)(velocity)
p = mv
measured in units of:
kilogram-meter/second
Law of Conservation of Momentum
states that: the total momentum of a group
of objects remains constant
in other words:
the total momentum of objects before a
collision equals the total momentum after
a collision.
Before the collision
0.3 kg
0.25 kg
8
C
1.5 m/s
0 m/s
p = (0.25 kg)(1.5 m/s)
p = (0.3 kg)(0 m/s)
p = .38 kgm/s
p = 0 kgm/s
pt = .38 kgm/s + 0 kgm/s
pt = 0.38 kgm/s
After the collision
0.3 kg
0.25 kg
C
8
0.75 m/s
0.63 m/s
p = (0.25 kg)(0.75 m/s)
p = 0.19 kgm/s
p = (0.3 kg)(0.63 m/s)
p = 0.19 kgm/s
pt = 0.19 kgm/s + 0.19 kgm/s
pt = 0.38 kgm/s