WHAT IS A FORCE????? PUSH A force is a push….. PULL … or a pull.
Chapter 12 Forces and Motion. Force Force is a push or a pull.
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Transcript of Chapter 12 Forces and Motion. Force Force is a push or a pull.
Chapter 12
Forces and Motion
Force
Force is a push or a pull.
Force
A force can cause:
A resting object to move
Accelerate a moving object By changing the object's
Speed
Direction
Measuring Force
Measuring Force
lbs - Pound
N - Newton
Connecting Motion and Forces
Force (newton, N): A push or pull one body exerts on another.
Earth
Balanced Forces
Balanced Forces: Forces on an object that are equal in size and opposite in direction.
Unbalanced Forces
Unbalanced Forces: Forces on an object are not equal resulting in a Net Force.
5 N 3 N
Unbalanced Forces
Unbalanced Forces: When an unbalanced force acts on an
object, the object accelerates.
5 N 3 N
Net Force
A Net Force on an object always changes the velocity of the object.
2 N
Balanced Forces
Balanced Forces: When the forces on an object are balanced, the net force is
zero and there is no change in the
object's motion.
Friction
Force that opposes the motion of objects that touch
as they move past each other.
Static Friction
A friction force that acts on objects that are not moving.
Sliding Friction
A friction force that opposes the motion of an object as it slides over a
surface.
Rolling Friction
Rolling Friction
A friction force that acts on rolling objects, caused by the change in shape at the
point of rolling contact.
Fluid Friction
AirResistance
Fluid Friction
Fluid Friction
A friction force that opposes the motion of an object
through a fluid.
Gravity
Gravity: Every object in the universe exerts a force on every other object. This force is Gravity!!!
Gravity
Gravity causes objects to accelerate downward, whereas air acts in the direction opposite to the motion and reduces acceleration.
Gravity
AirResistance
Projectile Motion
Projectile Motion
Projectile Motion
Vertical Component
HorizontalComponent
Projectile Motion
The combination of initial forward velocity and the
downward vertical force of gravity causes the ball to
follow a curved path.
Physical Science: 12-1
Worksheet: 12-1Due:3/4/04
Ari
stotl
e
Force was required to keep an object
moving at a constant speed.
Ari
stotl
e
Object will move indefinitely if no force is applied.
New
ton
New
ton
New
ton
Inertia
Inertia (mass): The tendency of an object to resist any change in its motion.
1kg 25 kg
The more mass an object has, the greater its inertia.
Newton’s First LawThe Law of Inertia
An object in moving tends to
stay in motion at a constant velocityand
an object at resttends to
remain at rest unless a net force acts on it.
Newton’s First Law
Newton’s Second Law of Motion
The Law of Acceleration
A net force acting on an object will accelerate that object in the
direction of that forceFa
Net Force Accelerates
FE
FE - engine
FF
FF - friction
FNet
FNet – net forceFNet = FE - FF
Net Force Accelerates
FE=25NFF =5N
FN
FN = FE - FF FN = 25N – 5N
FN = 20N
Newton’s Second Law
Acceleration
Force = mass x acceleration
F = ma
F
m a
F = ma
m= Fa
a=Fm
Example #1
A car with a mass of 2000kg is parked on the side of the road. How much force is needed to accelerate
the car at 3m/s²? (Assume that there is no friction
against the car.)
Example #1
F
Given: m = 2000kg a = 3m/s²
Find: F = ?
Equation: F = ma
F = (2000kg) x (3m/s²)F = 15,000N
Weight
Weight: The measure of the force of gravity on an object.
MassMass: The amount of matter making up an object.
Weight
Moon Earth Jupiter (16.7 lb) (100 lb) (254 lb)
Falling
Falling
All objects fall at the same rate!!
9.8m/s²
32ft/s²
22mph/s{Acceleration due to
Gravity!!!g
Falling
Acceleration due to
gravity.g
Force due to
gravity.W (weight)
W = mg
Falling
W
Fair
W = Fair
Terminal Velocity
Homework: 12-2
Worksheet: 12-2Due: 3/10/09
Homework: 12-3
Math PracticePage: 367, 1-4Due: 3/10/09
A boy pushes forward a cart of groceries with a total mass of 40.0 kg. What is the
acceleration of the cart if the net force on
the cart is 60.0 N? Given: Find:
Equation:
Solve:
What is the upward acceleration of a helicopter with a mass of 5000 kg if a force
of 10,000 N acts on it in an upward
direction? Given: Find:
Equation:
Solve:
An automobile with a mass of 1200 kg accelerates at a rate of 3.0 m/s2 in the forward direction. What is the net
force acting on the automobile?
(Hint: Solve the acceleration formula for force.) Given: Find:
Equation:
Solve:
A 25-N force accelerates a boy in a wheelchair at 0.5 m/s2 What is the mass of the boy and the
wheelchair?
(Hint: Solve Newton's second law for mass.) Given: Find:
Equation:
Solve:
Action and Reaction
Newton’s Third Law
When one object exerts a force on a second object, the second one exerts a force on the first
that is equal in size and opposite in direction.
For every action there is an equal and
opposite reaction.
Action and Reaction
Action - Reaction Pair
Rocket Propulsion
Reaction ForceRocket Accelerates
Action ForceEscaping Gases
Momentum - Mass on the Move
Momentum ( p unit:kg•m/s )A property a moving object
has because of mass and velocity.
v
v
Momentum Equation
momentum = mass X velocity
p = m x v
Example: A car with a mass of 2000 kg is moving with a velocity of 40 m/s. What is its’ momentum?Given: m = 2000 kg
v = 40 m/sFind: p = ?
Equation: p = m x v
Solve: p = 2000 kg x 40 m/s
p = 80,000 kg•m/s
Conservation of Momentum
The total momentum of a group of objects does not change unless
outside forces act on the objects.
The momentum before a collision is equal to the momentum
after the collision.
Total Momentum Before = Total Momentum After
Total Momentum Before = Total Momentum After
Momentum
Homework: 12-3
Worksheet: 12-3Due: 3/12/08
Universal Forces
d
Electromagnetic Forces
Electromagnetic forces are associated with charged particles.
Electric Forces
Magnetic Force
Magnetic Poles
Unlike Poles (North-South)
Attract!!!
Like Poles (North-North South-South)
Repel!!!
Nuclear Force
Two forces that act in the nucleus to hold it together.
Strong Nuclear Force
Weak Nuclear Force
Strong Nuclear ForceStrongest Force
Holds the nucleus together
Short Range
Weak Nuclear Force
Weaker than the Strong Force
Short Range
Gravitational Forces
Gravitational Forces
Any object with mass exerts a gravitation force.
Long Range
Gravitational Forces
Tides
Tides
Circular Motion
Sending up SatellitesV = 29,000km/h (18,000mph)
Sending up Satellites
Geostationary
Homework: 12-4
Worksheet: 12-4Due: 3/13/09