Download 01Forces Power Point

Forces
Forces affect Motion
• A force is a push or a pull
that changes an object’s
motion.
• This means that forces make
objects speed up, slow
down, or change direction.
• Forces also transfer energy
from one object to another
object like when you hit a
ball with a bat.
• The SI unit used to measure
force is the newton. (N).
 One newton is the
amount of force
needed to accelerate
a 1 kg mass by 1 m/sec2.
Gravity and Friction are Forces
 The force of gravity on an
object is called weight.
 Weight is different than mass.
 Mass is the amount of matter
in an object and weight measures
the force of gravity on that
mass.
 Mass does not change on
different planets, but weight
does, depending on how
strong the force of gravity is!
 The force of friction acts
to slow objects that are
already moving or make them
stop.
 Friction is caused when
objects rub together.
 There are three kinds of
friction: sliding, rolling,
and fluid friction.
Types of Friction
 Sliding friction - when two
objects slide over one another;
determined by object’s weight
and types of surfaces
 Rolling friction when an object rolls
over a surface; a
smaller force than
sliding friction for
similar objects
 Fluid friction - when an
object moves through a
fluid; the smallest force of
the three types of friction
for similar objects
Falling Objects
If no other forces act on Projectile motion is the
an object, gravity causes
curved path followed by
it to accelerate towards the
some moving objects.
center of the earth at 9.8 Projectile motion is
m/sec2.
caused by the two forces
At terminal velocity, the
of a horizontal push and
forces of friction and
downward gravity.
gravity are equal and
opposite on an object. Its
speed remains constant.
Balanced and Unbalanced Forces
• According to Newton’s
3rd Law, forces always
act in pairs.
• Forces may be balanced
(equal in amount and
opposite in direction).
• Balanced forces cause
no change in an object’s
motion.
• Forces can also be
unbalanced (opposite in
direction but unequal in
amount).
• Unbalanced forces do
change an object’s motion
(The racquet’s force makes
the ball reverse direction!
Net Force
• Net force is the sum of all the forces acting on an object.
• If the forces are acting in the same direction, add them
together to find the net force. Which way will the boats be
pulled? (Hint: Don’t forget direction.)
N
W
5N
E
A
S
15 N
Net force on A = _____
balanced or
unbalanced?
 If the forces are acting in the opposite direction,
subtract to find the net force.
4N
15 N
B
10 N
16N
C
12 N
Net force on B = _____
balanced or unbalanced?
Net force on C = _____
balanced or unbalanced?
Momentum and Circular Motion
Momentum is a way to
measure “inertia of
motion.” It tells how
hard it is to stop or start
an object’s movement.
Momentum = (mass)(velocity)
An object moving in a
circle has centripetal
acceleration.
Centripetal force is the
force needed to make an
object move in a circle.
Universal Forces
• There are four forces that work together to control the
universe as we know it. Some of these forces work over
very large distances and some can only be detected at
very small distances. The four forces are:
1.
2.
Gravitational Force - is 3.
the weakest of the
universal forces. It
depends on the mass
of the objects and the
distance between
them.
Electromagnetic Force - 4.
may attract or repel.
These are much stronger
than gravity.
Strong Force - holds the nucleus
of an atom together by binding the
protons and the neutrons.
Protons, neutrons, and electrons
are made of smaller particles
called “quarks.” Weak force glues the quarks together.
Quarks stuck
together to make a
proton