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Forces
Ch. 9.1
Types of Forces
Pearson
Online activity
Essential Question:
How Do Objects React to Forces?
What is force?
What are the Main types of Forces?
What Factors affect Gravity?
Review….
Acceleration- is the rate at which velocity changes with time.
Equation= Final speed- initial speed
time
Velocity= Speed in a given direction
Speed= is the distance an object travels in a given direction
Equation= Distance
time
Vocabulary 9.1
1. A force: is a push or a pull
2. Applied force: is a force that is put on an object by another object.
3. Normal force: is the force that acts between objects when they are in
contact with each other.
4. Friction is the force that two surfaces exert on each other when they rub
against each other.
5. Electrical Force is the force between two charged objects.
6. magnetic force the attraction or repulsion between magnetic poles.
7. Gravitational force, or gravity, is a force that pulls objects toward each
other.
8. The law of universal gravitation states that the force of gravity acts
between all objects in the universe that have mass.
9. Weight is a measure of the force of gravity on an object.
10. Mass is a measure of the amount of matter in an object. Mass
Force
Force- a push or a pull.
i.e.
A force can propel the men into the pool.
Applied Force- A force that is put on an object by another
object.
i.e.
When she used applied force, she was able to open the container
Gravitational force- A force that pulls objects toward each
other.
i.e.
Gravitational force pulled the paper toward the floor when it blew off the
table.
Inertia- Resistance to change in motion.
i.e.
A roller coaster’s inertia makes it hard to stop.
Pg. 329
What is force?
1 objects pulls/pushes another
object, then the 1st object exerts
(applies) a force on the 2nd.
Force is described by its strength
and direction.
S.I unit for force= NEWTON (
after Sir Isaac Newton)
WHAT IS FORCE?
A force is a push or a pull.
When one object pushes or pulls another object, the first object exerts a
force on the second object.
EXAMPLE:
You exert a force on a chair when you pull it away from a table.
Like velocity and acceleration, a force is described by its strength and
by the direction in which it acts.
Pushing left is a different force from pushing right.
The direction and strength of a force can be represented by an arrow. The
arrow points in the direction of the force.
The length of the arrow tells you the strength of the force.
The strength of a force is measured in an
SI unit called the newton (N).
2 Main Types of Forces
Every day you are using forces to act on objects.
The
2 main types of forces are:
contact forces
forces that act at a distance.
Contact forces include: applied forces, the normal force, and
friction.
force act at a distance include: Electrical force, magnetic force,
and gravitational
Types of Force pg. 330
Two main types of forces:
1.Contact forces(push or force on an object
through physical contact.)
friction
2.
Forces that act at a distance-
types of surfaces
how hard the surfaces
are pushed together
Friction pg. 331
•Brainpop
•Friction-The force that two surfaces exert (use) on each other when they
rub against each other.
Factors that affect (change) the force of friction
friction
types of surfaces
how hard the surfaces
are pushed together
Friction comes from the Greek word- Fricare
Main types of forces
To feel the effects of contact forces, an object must touch
another object.
An applied force is a force that is put on an object by another
object.
The normal force is the force that acts between objects when
they are in contact with each other.
Normal here means perpendicular. This force acts perpendicular
to the surface of contact such as the wall that pushes back
and supports you when you lean against it.
Did You Know?
The Daytona 500 is tires on the
race cars can heat up to 93one
of the biggest racing events in
the world. Cars race along the
track at over 322 km/h (200
mph). This kind of speed
generates so much friction that
the degrees Celsius (200
degrees Farenheit).
Forces acting at a distance pg. 332
Some forces push or pull an object without touching the object.
Types of forces at a distance:
1.Electrical force- forces between charged objects
positive(+) charge= proton
negative (-) charge= electron
If a proton= + which carries a positive charge , is near an electron, which carries a negative charge,
they attract one another.
1.Magnetic Force- The attraction or repulsion between magnets
poles.
2.Gravitational Force- A force that pulls objects toward each other
(force that pulls objects straight down toward the center of the Earth)
Magnetic Poles
Positive +
Magnetic force
Law of Gravitation
The law of universal gravitation states that the force of gravity
acts between all objects in the universe that have mass.
So, any two objects in the universe that have mass attract each
other.
For example:
you and your pencil are attracted to each other. However, you do
not notice the attraction between such small objects as you
and your pencil because these forces are extremely small
compared to the force of Earth’s attraction. You observe only
the effects of the strongest gravitational forces.
Factors that Affect Gravity pg. 333
Gravity acts everywhere in the universe (not just on Earth)
i.e.
• Skydivers fall to the ground
• Moon orbiting around Earth
• Keeps all planets orbiting around the sun
Law of Universal Gravitation--- The scientific law that states that
every object in the universe attracts every other object.
Any 2 objects that have mass (how much matter is in an object) attract
each other.
Factors Affecting Gravity pg. 334
Brainpop- Gravity
G.F. is present in any 2 objects in the universe
Two factors that affect gravitational attraction are
_______________ and _______________.
The more mass an object has, the greater its gravitational force.
The shorter the distance is between two objects, the stronger
the gravitational force between the objects.
Bigger mass= greater gravitational force between objects.
As distance increases between objects= (-) less gravitational force
S.I. Unit
Mass = Kilogram
Weight and Mass pg. 335
Weight is a measure of the force of gravity on an object.
Mass is a measure of the amount of matter in an object.
• Mass is the same on Earth as it would be on any other planet.
• But weight would vary on each planet, since each planet’s
gravitational force is different.
At any given time, mass stays the same (amount of matter in an
object) BUT weight varies with the strength of _________
___________________.
Types of Forces
Gravitational
Attraction
Gravitational
attraction depends
on two factors:
mass and
distance. Compare
the gravitational
force between
different planets
and their sun.
Types of Forces
Weight and Mass
The Mars Phoenix Lander weighs about 3,400 N on Earth. It weighs about
1,300 N on Mars. If the dog weighs
60 N on Earth, what would he weigh on Mars and the moon?