Download Matter in Motion Ch.5

FORCES
Ch.10
“May the Force be with You”
I. Force
All
forces are exerted by one
object on another object.
For any push to occur
something has to receive the
push.
Newton (N)
The
SI unit scientists use to
measure force.
I. Force
A
force is: A push or a pull.
 All forces have both size
(magnitude) and direction.
 more Newtons = more force
Net Force
Net
Force is The force that
results from combining all the
forces exerted on an object.
The
motion of an object will be
determined by net force
Net Force
UNBALANCED
FORCES **net force
is greater
than zero
**causes a
change in
the object’s
velocity
(acceleration)
Net Force
BALANCED FORCES
** the object’s motion does
not change
**net forces equals zero
II. Friction
A
force that opposes motion between
two surfaces that are touching.
 Rougher
friction.

surfaces create more
Greater forces create more friction.
 Friction
results in heat (objects that
rub together, heat up)
. Types of Friction
1.
Static Friction
2. Sliding Friction
3. Fluid Friction
4. Rolling Friction
III. Gravity
The
force of attraction between
objects that is due to their
masses.
All matter has mass!
Therefore…???
IV. Law of Universal
Gravitation
 This
law
describes the
relationship
between
gravitational
force, mass, and
distance. This
law was worked
out by Newton.
IV. Law of Universal
Gravitation

1. Gravitational force is small between
objects with small masses.

2. Gravitational force is large between
objects with large masses.
IV. Law of Universal
Gravitation

3. The larger the distance between two
objects, the smaller the gravitational
force is between them.
V. Weight
 The
measure of the gravitational force
exerted on an object.
 Weight
is measured with a spring scale.
 Weight
= mass X acceleration
VI. Mass
The
amount of
matter in an
object.
Mass
is measured
with a balance.
VII. Gravity & Motion

1. FREE FALLacceleration of a
falling object due to
the pull of gravity
only.

2. AIR RESISTANCEfluid friction of air
acting on an object
falling through air
VII. Gravity & Motion

3. PROJECTILE MOTION - is motion of a thrown
object. Two forces act on it. One is the force of
the throwing motion (horizonal) and the other is
the force of gravity (vertical)
Orbiting objects
Objects in orbit
are in projectile
motion
VIII. Elastic Forces
Matter is elastic if it
returns to its original
shape after being
squeezed or stretched
 Compression is the
elastic force when an
object is pushed
together.
 Tension- is the elastic
force that stretches or
pulls an object

IX. Newton’s Laws

Isaac Newton (1642-1727) described 3
important laws that help us understand
forces. These laws seem simple and
obvious to us and we tend to take them
for granted. Almost every aspect of our
lives involves one or more of them.
Newton’s
 An
st
1
Law of Motion:
object will remain at rest or
moving at a constant velocity
unless it is acted upon by an
unbalanced force
Newton’s
 “An
st
1
Law of Motion:
object in motion will stay in
motion, an object at rest will
stay at rest unless acted upon
by an outside force.”
Newton’s
st
1
Law of Motion:
 1.
An unbalanced force will cause
an object to speed up, slow down
or change direction
 2.
Inertia is the tendency of an
object to resist a change in
motion
Newton’s
st
1
Law of Motion:
 3.
Inertia depends on the mass
of an object.
 The
greater the mass, the greater
the inertia and the greater the
force required to change the
motion.
Newton’s
nd
2
 Acceleration
Law of Motion:
depends on the
net force acting on the object
and the object’s mass
Newton’s
 “When
nd
2
Law of Motion:
a force is applied to an
object, the object accelerates in
the direction of the applied
force. The acceleration is less
when the mass of the object is
greater.”
Newton’s
nd
2
Net force =
Acceleration
mass
OR
Law of Motion:
net force = mass X acceleration
ex: Think of kicking a football and a rock the size
of a football. You would need a lot more force
to move the rock the same distance as the
football.
Newton’s
 If
rd
3
Law of Motion:
one object exerts a force on
another object, the second
object exerts a force of equal
strength in the opposite
direction on the first object
Newton’s
 “For
rd
3
Law of Motion:
every force (action) there
is an equal and opposite force
(reaction). If you push or pull
on an object, the object will
push or pull back with equal
and opposite force.”
X. Momentum
 A. depends on mass and velocity
 B. Momentum is described by size and
direction
 C. Momentum = mass X velocity
 D. The more momentum an object has
the harder it is to change it’s velocity
XI. Conservation of Momentum
the
total momentum of a
group of objects stays the
same, or is conserved, unless
outside forces act on the
objects
XI. Conservation of Momentum

A. Collisions of 2 moving objects – the
momentum of one object decreases and
the momentum of the other object will
increase

B. Collision of 1 moving object (with a
stationary object)– the momentum of the
moving object is transferred to the other
object