Download Forces and Motion

FORCES AND MOTION
HOW DO FORCES AFFECT OBJECTS?
• Force- a push of pull that one object
exerts on another.
• Forces can change the motion of the
object.
• A baseball batter uses force to hit the ball
and that hit changes the direction of the
ball.
• Forces can also change the shape of
objects.
• You use force to crush a soda can.
HOW DO YOU MEASURE FORCES?
• To measure force we use a spring scale.
• Measured in Newtons
• Friction- a force that opposes the
motion of the object sliding over
another.
• If you pull an object with a spring scale
along a surface, you can feel the object
resist the sliding.
WHAT ARE THE TYPES OF FRICTION?
• Friction acts anytime the surfaces of
objects are in contact.
• 3 kinds of friction:
• Sliding Friction: When opposite forces push
across.
• Static Friction: Prevents the start of any
movement between surfaces in contact. If the
surface is smother or steeper, there might not
be enough to hold an object in place.
• Rolling Friction: Friction allows wheels to move
us forward. Friction between wheels and the
ground push an object ahead.
HOW DO DRAG FORCES ACT?
•
Drag Motion- when an object moves
through a gas, like air, or any liquid, there
is a force that opposes motion.
•
The object moves through air, the air
molecules bump into it, which causes the
object to slow down.
•
Similar to sliding friction because they both
oppose motion.
•
Drag force depends on speed, size, and
shape.
•
Speed: the faster the speed the greater the
drag.
HOW DO OBJECTS ATTRACT?
• Gravity- a force of attraction that occurs between
any object that has mass.
• Gravity is a force that only pulls.
• The larger the mass of an object, the more
gravitational pull it has.
• The Earth’s gravity is much larger than a person’s, so we
can feel the gravity of the Earth more than we can feel
the gravitational pull of others.
WHAT AFFECTS GRAVITY?
• The force of gravity between two objects
depends both on the masses of the two objects
and the distance between the objects.
• The closer the objects are to each other, the
stronger the force of gravity they exert on each
other.
• Weight- is the force of gravity between the
Earth and the object.
• Weight is measured on a scale.
• Each planet pulls on an object’s mass differently
which affects its weight.
WHAT ARE BALANCED FORCES?
• Net Force- combined effect of the
forces acting on an object.
• When the forces acting on an object are
equal the net force is 0 and the object
doesn’t move.
• Anytime two or more forces completely
offset one another, we say they are
balanced forces.
• When the forces on an object are
balanced, the net force on the object is
zero.
WHAT ARE UNBALANCED FORCES?
• Unbalanced forces- When the force or forces
acting on an object do not completely offset one
another.
• The leftover force can be represented as a single
push of pull in a certain strength and direction.
• When a net force is unbalanced, it means the net
force is not at zero.
WHAT IS NEWTON’S FIRST LAW?
• Newton’s First Law of Motion- “An
object in motion tends to stay in motion,
and an object at rest tends to stay at
rest.”
• An object’s velocity can only be
changed by applying a force to it.
• Motion can only be changed by
applying a force.
• Inertia- the tendency of an object to
oppose any change in motion.
HOW DOES INERTIA AFFECT YOU?
• Jolting forward when a bus stops quickly
is only one way you tend to keep moving
because of inertia.
• Inertia is why seatbelts are so important.
• You might be able to control yourself in a car
when you know it is going to make a turn, it is
almost impossible to control your movement in
a car that suddenly stops or changes
direction.
• Seatbelts keep you moving with the car or
stop you from moving when the driver breaks.
WHAT MAKES OBJECTS TRAVEL IN A CIRCLE?
• An object that is traveling in a circle is
accelerating even if it moves at a steady
speed.
• It accelerates because its direction of travel is
constantly changing.
• The pull of a string keeps the object
moving.
• Once the string breaks, there will no longer
be any unbalanced force on the object. Its
inertia will carry it straight ahead at a
constant speed.