Forces and motion powerpoint

• Define force and give examples and non-examples of force.
• Describe the different types of forces and classify those forces as contact or noncontact forces.
• Describe applied force and classify applied forces as pushes or pulls.
• Define friction and describe how difference surfaces exert more or less friction.
• Describe gravitational force and how gravity is important to how the universe works.
• Compare and contrast weight and mass. Calculate weight using the mass and gravitational force of a planet or star.
• Describe buoyancy and determine whether an object will float or sink in a fluid.
• Compare spring force in a compressed and stretched spring. Describe tension and its direction in a rope, string or
wire.
• Identify balanced and unbalanced forces and describe what happens when balanced or unbalanced forces act on an
object.
• Describe the motion of an object and why an object moves.
• Describe five patterns of motion and identify examples of those patterns of motion.
• Illustrate and determine net force on an object and how net force will affect the motion of the object.
• Calculate velocity and acceleration so to determine how an object’s position and speed changes over time as it
moves.
• Describe Newton’s three Laws of Motion and identify examples of each law.
• Describe momentum and inertia and apply the concepts to a moving object.
• Describe the relationship between force, mass and acceleration using the equation F = ma.
• Describe what happens during a collision and how Newton’s Third Law of Motion applies to collisions.
• Compare and contrast vector and scalar quantities. Classify different values as vector or scalar.
© Stephanie Elkowitz1Forces & Motion

• What is Force?
• Types of Forces
• Air Resistance
• Gravity & Weight
• Other Forces (Tension, Spring, Buoyancy, Normal)
• Balanced vs. Unbalanced Forces
• Net Force
• What is Motion?
• Describing Motion
• Velocity & Acceleration
• Graphing Velocity & Acceleration
• Patterns of Motion
• Newton’s Laws of Motion
• Inertia
• Momentum
• Calculating Force
• Collisions

• A force is a push or a pull on an object.
• All forces have strength and direction.
• The strength of a force is measured in Newtons (N).
• A force results when two or more objects interact. When the
objects stop interacting, there is no more force.
• Objects do not have to physically touch each other to exert
force on the other.

• There are three important characteristics of all forces:
1. All forces have magnitude or strength.
2. All forces have direction.
3. All forces are measured in Newtons (N).

• An object that exerts force
repels or attracts other
objects.
• When we say an object
repels another object, it is
exerting a pushing force
against the object.
• When we say an object
attracts another object, it is
exerting a pulling force on
that object

• Some forces result when two objects physically touch each
other. These forces are called CONTACT FORCES.
• There are six important contact forces:
1. Applied Force
2. Friction
3. Spring Force
4. Tension
5. Normal Force
6. Buoyancy

• An applied force is a force applied by a person or object onto
another object.

• Friction is a force that opposes motion. It works in the
opposite direction of a moving object.

• Spring force is a force created by a stretched or compressed
spring.

• Tension is created when two objects pull on a rope, string, wire
or cable in opposite directions.

• The normal force is a force
exerted by a surface on an
object resting on that surface.
• On a level surface, the normal
force is equal and opposite to
the weight of the object.

• A fluid pushes upward on an
immersed object. This force is
called buoyancy or buoyant
force.

• Some forces result when two objects do not physically touch
each other. These forces are called NON-CONTACT FORCES.
• There are three important non-contact forces:
1. Gravitational Force (Gravity)
2. Electric force
3. Magnetic force

• Gravity, or
gravitational force, is
a force of attraction
between two objects.

• Electric force is an invisible
force created by electrically
charged particles.
• Only electrically charged
particles produce electric
force.
• Particles with an electric
charge are attracted to or
repelled by other particles
with an electric charge.
© Stephanie Elkowitz15Magnetism & Electricity
+
−
POSITIVE CHARGE
NEGATIVE CHARGE

• Magnetic force, or
magnetism is a force
created by magnets.
• Only magnets produce
magnetic force.
• Magnetic force attracts or
repels magnetic objects
or magnets.
© Stephanie Elkowitz16Magnetism & Electricity

• An applied force is a force applied by a person or object onto
another object.
• An applied force can change the motion of an object. It can
cause an object to move in the same direction as the force. It
can also slow or stop a moving object.

• An applied force can be a push or a pull.
• A push is applying a force that causes the object to move away
from the object or person that is pushing.
• A pull is applying a force that causes the object to move
towards the object or person that is pulling.

• More than one applied force can act on an object or person.
• When this occurs, the motion of the object or person will be
determined by the magnitude and direction of each applied
force.
• This is one reason why it is important to note the direction of
an applied force. We usually denote the direction of an applied
force with an arrow.

• Friction is a force that opposes motion. It works in the
opposite direction of a moving object.
• Friction is a force you must overcome to move a stationary
object.
• Friction is a force that causes moving objects to slow down.

• The force of friction exerted by a surface depends on the
smoothness of the surface.
• A smooth surface exerts less friction than a rough surface.
• The surface of objects can be coated with liquid to reduce
friction. Liquid makes the surface smoother. This is why oil is
important to a car engine. The oil decreases friction between
the rubbing parts in the engine.

• Only solids exert friction.
• Gases and liquids resist
motion. This resistance is
called drag.
• Air resistance is a type of
drag. It is like “air friction.”
• The direction of air resistance
opposes the direction of
motion.
• Air resistance slows falling
objects. It also slows an
object moving through air,
like planes and cars. © Stephanie Elkowitz22Forces & Motion

• Air resistance does NOT depend on the mass of an object.
• Air resistance depends on the speed, shape and orientation of
an object moving through air.
• A fast moving object experiences more air resistance than a
slow moving object.
• An object shaped and orientated so it has more surface area in
contact with air experiences more air resistance.
• Planes are streamlined to reduce air resistance. This allows
them to fly faster through the air.
• Parachutes are large so to “capture” more air resistance.
Parachutes slow the downward movement of an object
through air.

• Gravity, or gravitational
force, is a force of attraction
between two objects.
• All objects with mass exert a
gravitational force.
• Larger objects exert a
greater gravitational force.
• We only notice the
gravitational force of very
large objects, such as stars
and planets.

• Gravity is the force that attracts objects to Earth. It pulls
objects towards the center of Earth.
• Earth’s gravity also keeps the moon in orbit around Earth.

• The force of gravity decreases when the distance between objects
increases. This explains why the moon does not fall to Earth’s
surface, but objects in Earth’s lower atmosphere do. The moon is
238,900 miles away from Earth! At this distance, the strength of
Earth’s gravity is strong enough to keep the moon in orbit but not
so strong that the moon crashes to Earth’s surface.
Why doesn’t
gravity cause
the moon to
crash into
Earth?

• The sun’s gravity keeps Earth and other planets orbiting
around sun.
• The Earth is at the perfect distance from the sun (based on its
mass and other factors). The sun’s gravity keeps Earth in orbit
but does not pull Earth so much that the planet crashes into
the sun.

• Weight is the result of gravity pulling on an object.
• Weight is NOT the same as mass.
• Mass is the amount of matter in an object. Mass is measured
in kilograms (kg).
• Weight is a measure of gravity’s effect on mass. Weight is
measured in Newtons (N).

• The force of gravity is much less on the moon because the
moon is much smaller than Earth. Because gravity is less, a
person’s weight is less. A person can jump higher using the
same amount of force as he would use on Earth since he has to
overcome a lesser force of gravity (weight).
Why can an
astronaut
jump so high
on the
moon?

THINK ABOUT IT...
The force of gravity is greater on Jupiter because Jupiter is larger
than Earth.
Would a person’s weight on Jupiter be greater, less than or the
same as his weight on Earth?
Would a person’s mass on Jupiter be greater, less than or the
same as his mass on Earth?

THINK ABOUT IT...
The force of gravity is greater on Jupiter because Jupiter is larger
than Earth.
Would a person’s weight on Jupiter be greater, less than or the
same as his weight on Earth?
IT WOULD BE GREATER.
Would a person’s mass on Jupiter be greater, less than or the
same as his mass on Earth?
IT WOULD BE THE SAME.

You can calculate weight using the equation:
Weight (Fg) = Mass (m) × Gravity (g)
Gravity on Earth is 9.8 m/s2
Example:
Mass = 10 kg Weight = Mass × Gravity
Gravity = 9.8 m/s2 Weight = 10kg × 9.8 m/s2
Weight = 98 N

TRY IT:
What is the weight of a 50 kg person on Earth? On the moon?
Formula: Fg = m × g
Gravity on Earth = 9.8 m/s2
Gravity on Moon = 1.6 m/s2

TRY IT:
What is the weight of a 50 kg person on Earth? On the moon?
Earth: Moon:
Fg = m × g Fg = m × g
Fg = 50 kg × 9.8 m/s2 Fg = 50 kg × 1.6 m/s2
Fg = 490 N Fg = 80 N
Formula: Fg = m × g
Gravity on Earth = 9.8 m/s2
Gravity on Moon = 1.6 m/s2

• A fluid pushes upward on an
immersed object. This force is
called buoyancy or buoyant
force.
• Buoyant force is directly related
to the density of the fluid and
how much fluid is displaced, or
moved, by an immersed object.

• Denser fluids exert a greater
buoyant force.
• For example, saltwater is denser
than freshwater. It is easier to
float in the ocean that a pool or
lake because saltwater is
denser. In the Dead Sea, anyone
can float easily because the
water is super-salty. Super-salty
water is very dense!

• If buoyancy is equal to or
greater than the weight of an
immersed object, the object
will float.
• If buoyancy is less than the
weight of the object, the
object will sink.

• Life jackets or vests help keep a
person afloat in water. A life jacket
is filled with trapped air. When the
jacket is submerged in water, the
jacket displaces some water. The
trapped air in the life jacket weighs
much less than the water it
displaces. So, water pushes up
harder than the life jacket pushes
down. This creates buoyancy.
• When worn by a person, the life
jacket essentially decreases the
weight of a person. It provides
buoyancy (buoyant force) to keep
the person afloat.

• Large ships stay afloat because
they have very large, u-shaped
hulls.
• A large hull displaced a large
amount of water. This increases
buoyant force and thus, keeps
the boat floating.
• Video about why ships float:
https://safesha.re/gtk
(Original link: https://youtu.be/CvWrkxzCiaY)

• Tension is created when two objects pull on a rope, string, wire
or cable in opposite directions.
• Tension is the force created in the wire when objects pull on
the wire. Tension pulls on the objects equally towards the
center of the wire.
• If a person pulls on a wire anchored to a wall, tension in the
wire pulls back on the person towards the wall.

• When an engineer designs a structure that includes cables and
wires, such as a bridge, the engineer must consider the amount
of tension applied to the structure.
• The engineer must make sure the cables and wires can
withstand tension when force is applied to the structure.

• Spring force is a force created by a
stretched or compressed spring.
• A spring is a metal, helical coil. It
can be pressed or pulled apart but
wants to return to original shape
when released.
• A spring can be positioned as a
neutral, stretched or compressed
spring.

• A neutral spring is a spring that is not stretched or compressed.
• When a spring is compressed, it wants to push outwards to its
neutral/resting position.
• When a spring is stretched, it wants to pull inward to its
neutral/resting position.

• Cars depend on springs for shock
absorption.
• Springs are pushed and pulled in
response to bumps on the road
surface and vibrations created
while driving.
• Spring force balances the car and
makes handling of a car smoother
and more comfortable. It also helps
protect the car and keep
passengers safe because driving is
easier when driving is smoother.

• More than one force can act on an object at the same time.
• The forces can act in the same or opposite directions.
• The combined result of all forces acting on an object is called
net force.

• When the forces acting on an object are equal and balanced,
we say the forces are balanced.
• When balanced forces act on an object, the object’s motion
does not change. If the object is at rest, it will stay at rest. If
the object is moving, it will continue moving in the same
direction with the same speed.

• When the forces acting on an object are NOT equal and
balanced, we say the forces are unbalanced.
• When unbalanced forces act on an object, its motion will
change. The object’s speed, position or direction will change.
• The change in an object’s motion depends on the net force
acting on the object and the mass of the object.

• Airplanes can fly because of the
shape of their wings. When a
plane propels forward, the wings
move through the air. Air that
moves under the wing creates an
upward force called lift.
• The faster the plane moves, the
greater the upward force (lift).
When lift is greater than the force
of gravity acting on the plane
(weight), the plane elevates in the
sky.
• Airplanes adjust their speed and
the shape of the wing to rise, stay
steady or lower in the sky.
Gravity
(weight)
Lift

• Motion is the movement of an object.
• An object moves when unbalanced forces act on the object.
• Pushing or pulling an object will change an object’s position
and/or direction.

• If you apply a force in the opposite direction of the object’s
motion, you can slow down and stop the object.
• If you apply a force is the same direction as the object’s
motion, you can increase the speed of the object.
• If you apply a force perpendicular to the direction of the
object’s motion, you can cause the object to turn (change
direction).

• Two unbalanced forces acting on an object can cause an object
to move as well. The object will move in the direction of the
larger force.
• The amount of motion created by unbalanced forces depends
on the difference in size of the forces. A greater difference in
force means the forces are more unbalanced. More motion is
created when the forces are more unbalanced.

• The motion of an object is described with respect to some
other object or position.
• The motion of an object is described by its position, direction
of motion and speed.
– Position: on top of, next to, over, under
– Direction: up/down, left/right, north/south
– Speed: miles per hour (mph), meters per second (m/s)

• Some objects move in an
expected or cyclical way
• Patterns of motion can
help you predict the
position, speed and
direction of an object
• Examples
– Sliding/Linear Motion
– Spinning/Rotation
– Circular/Revolution
– Rolling
– Periodic (swinging,
rocking, vibrating)
Periodic Motion

• Sliding/Linear Motion
– Motion along a straight line or
path
• Spinning/Rotation
– Movement of an object
around a fixed point
• Circular/Revolution
– Movement of one object in a
circular path around a second
object
• Rolling
– Combination of linear motion
and rotation; an object spins
as it moves along a straight
path

• Periodic Motion
– A group of motion patterns
– A motion that recurs over and
over in a regular and
repeating way
– Examples: rocking, bouncing,
vibrating, swinging

• Recall: The combined result of all forces acting on an object is
called the net force.
• When net force is zero, forces are balanced and the object’s
motion does not change.
• When net force is any value other than zero, the object’s
motion changes.

• Free-body diagrams help us calculate net force. They illustrate
forces acting on an object.
• If two forces are acting on an object in opposite directions, the
net force is the difference between the two forces. The
direction of net force is in the direction of the stronger force.
Net Force = 10 N – 5 N
Net Force = 5 N to the RIGHT

• Recall: The normal force is a force
exerted by a surface on an object
resting on that surface.
• On a level surface, the normal force is
equal and opposite to the weight of the
object.
• The normal force explains why a book
resting on a table does not move. The
force of gravity pulls the book down to
the surface. The normal force acts in an
equal and opposite direction so that
the book does not move.

• Velocity describes the speed and direction of an object’s
motion
• Speed is the distance traveled in a certain amount of time
• Direction is the way or path an object moves
• You can calculate velocity using the equation: velocity
(v) = distance (d) ÷ time (t)
• Velocity is measured in meters/second (m/s)
EXAMPLE:
A car travels east 100 meters in 2 seconds.
Velocity = distance ÷ time
Velocity = 100 meters ÷ 2 seconds
Velocity = 50 m/s east

• Acceleration describes the change in an object’s velocity
• Objects that speed up have a positive acceleration
• Objects that slow down have a negative acceleration (this
is also called deceleration)
• You can calculate acceleration using the equation: acceleration
(a) = change in velocity (v) ÷ time (t)
• Acceleration is measured in meters per second2 (m/s2)
EXAMPLE:
A plane’s velocity changes from 0 to 100 m/s in 5 seconds.
Acceleration = change in velocity ÷ time
Acceleration = (100 m/s – 0 m/s) ÷ 5 seconds
Acceleration = 20 m/s2

• Graphs can be used to describe the motion of an object
• A distance vs. time graph shows velocity
• A velocity vs. time graph shows acceleration
• What do the following graphs show?

Zero velocity
because there’s no
change in distance
over time
Constant velocity
because distance
directly increases
over time
Increasing velocity or
acceleration because
distance exponentially
increases over time
Zero acceleration
because velocity
does not change
over time
Positive acceleration
because velocity
increases over time
Negative acceleration
(deceleration) because
velocity decreases over
time

• Isaac Newton was a scientist
and mathematician who
lived 1643 – 1727.
• He developed three laws of
motion to describe how
forces interact with objects
and cause motion.
• Newton also made important
findings about gravity and
how to calculate the
gravitational force between
two objects.

What does this mean?
This means that objects
want to keep on doing what
they are doing. Objects
resist changes to their state
of motion. If there are no
unbalanced forces, an
object will maintain its state
of motion.
An object at rest will
remain at rest unless
acted on by unbalanced
forces. An object in
motion continues in
motion with the same
speed and direction
unless acted on by
unbalanced forces.

This means that more force
is needed to move heavier
objects. This law also
explains what happens
when you apply an equal
force to a heavy and a
lightweight object – the
lightweight object moves
(accelerates) more.
This law establishes the
equation F = ma.
An object accelerates
when a force acts on an
object with mass. The
greater the mass of the
object being accelerated,
the more force needed to
accelerate the object.

• Example: If a boy applies the same force to each wagon, the
wagon that has twice as much mass will accelerate half as fast.
It would take twice the amount of force to accelerate the
wagon with 20 kg the same as the wagon with 10 kg.

This means there is a force
equal in size but opposite in
direction for every force. In
other words, when one
object pushes on a second
object, the second object
pushes back on the first
object in the opposite
direction equally hard.
For every action
there is an equal
and opposite
reaction.

• Example: When a
rocket blasts off, the
force of its powerful
engines pushes down
on Earth’s surface.
This is the action. The
reaction is that
Earth’s surface pushes
the rocket upward
with an equally strong
force. This causes the
rocket to move
upward into space.

• Newton’s 1st law is also called the “Law of Inertia.”
• Inertia is the tendency to resist change in motion.
• Inertia explains why it takes time for a car to come to a stop. A
car moving forward wants to continue its motion. When the
driver pushes on the breaks, the car and the passengers inside
the car want to continue moving forward.

• During a car accident, the vehicle
(and passengers in the vehicle)
have inertia. When a car comes to
an abrupt stop, the vehicle and
passengers in the vehicle want to
continue moving forward. The
vehicle will crumple against the
object(s) it crashes into to, forcing
it to come to a stop. However,
passengers will continue to move
forward.
• Seatbelts help keep passengers
from being ejected from the
vehicle. Seatbelts apply a force
against passengers so they stay
within the vehicle.

• Momentum is the quantity of motion an object has.
• The momentum of an object depends on the object’s mass and
velocity.
• A heavy and fast moving object has more momentum than a
lightweight and slow moving object.
• More force is needed to change the motion of a heavy and fast
moving object than a lightweight and slow moving object
because it has more momentum.

Two football players are running
down the field with the same speed.
One player has a mass of 70 kg. The
other has a mass of 100 kg.
Which player has more momentum?
Which player is harder to tackle?

Two football players are running
down the field with the same speed.
One player has a mass of 70 kg. The
other has a mass of 100 kg.
Which player has more momentum?
The 100 kg player.
Which player is harder to tackle?
The 100 kg player because he has
more momentum.

• Newton’s Second Law tells us that the strength of force is
directly related to an object’s mass and acceleration.
• You can calculate the force of an object using the equation:
Force (F) = Mass (m) × Acceleration (a)
• This equation tells us the force of an object depends on how
massive the object is and how much the object is accelerating.
• Objects with a greater mass have greater force.
• Objects with a greater acceleration have greater force.

A truck has a mass of 2,000 kg. It is accelerating 20 m/s2. What is
the truck’s force?
A car has a mass of 1,500 kg. It is accelerating at 20 m/s2. What is
the car’s force?

A truck has a mass of 2,000 kg. It is accelerating 20 m/s2. What is
the truck’s force?
F = m × a F = 2,000 kg × 20 m/s2
F = 40,000 N
A car has a mass of 1,500 kg. It is accelerating at 20 m/s2. What is
the car’s force?
F = m × a F = 1,500 kg × 20 m/s2
F = 30,000 N

• A collision is an interaction between two objects that physically
come into contact with each other.
• A collision does not necessarily involve an accident – it is any
event where two objects bump into each other.

• Newton’s 3rd Law describes what happens during a collision.
The force exerted by one object is equal and opposite to the
force exerted by the second object.
• Example: If a pool stick collides with a pool ball, the force
exerted by the stick onto the ball is equal and opposite to the
force exerted by the ball onto the stick.

• Momentum is conserved during a
collision.
• This means the total momentum
of the two objects before the
collision equals the total
momentum of the two objects
after the collision.

• If momentum is conserved and
the mass of each object stays
the same, the velocity of the
objects must change.
• This explains why the speed
and/or direction of movement
changes for one or both objects
during a collision.
Remember...
The momentum of an object
depends on mass and velocity.

• Physics involves a lot of math.
Some quantities are pure
numerical values and are
described with magnitude only.
• Other quantities are described
by magnitude and direction as
well.

• Scalar quantities are fully described by magnitude alone.
• Scalar quantities only have a numerical value.
• Scalar quantities do NOT have direction.
• Examples:
– Speed
– Distance (or length)
– Energy
– Temperature
– Mass
– Time

• Vector quantities are described by magnitude AND direction
• Vector quantities have a numerical value and direction.
• We often refer to vector quantities as vectors
• Examples:
– Velocity
– Acceleration
– Displacement (the overall change in an object’s position)
– Force
– Weight
– Momentum

• Like a scalar quantity, we use a number to represent the
magnitude of a vector quantity.
• There are two ways to describe the direction of a vector
quantity:
1. You can use a positive and negative symbol to represent
vectors that act in opposite directions. For example, you
could describe an upward force with a positive symbol and
a downward symbol with a negative symbol.
2. You can use cardinal directions (north, south, east and
west) to describe the direction of a vector quantity.

• When drawing an illustration of vectors, like forces, we use
arrows to describe the direction of each vector.
• Example: When drawing a free-body diagram, we use arrows
to show the direction of the forces acting on an object. We use
positive and negative numbers to calculate the net force acting
on the object.
Net Force = 10 N – 5 N
Net Force = 5 N to the RIGHT

• Understanding that distance is
a scalar quantity and
displacement is a vector
quantity is important in
physics.
• Distance is a scalar quantity
that refers to "how much
ground an object has covered"
during its motion.
Displacement is a vector
quantity that refers to "how far
out of place an object is” or its
overall change in position.

• Example: A boy runs one lap around a 400 meter track. What
distance did he run? What is his displacement?

• Example: A boy runs one lap around a 400 meter track. What
distance did he run? What is his displacement?
– He ran a distance of 400 meters.
– His displacement is ZERO meters. Displacement is zero
because there was no change in his position.

• Images obtained from commons.wikimedia.org and the Public
Domain
• Clipart by:
– Stephanie Elkowitz
– www.mycutegraphics.com
– www.mysweetclipart.com
© Stephanie Elkowitz89Atoms & Reactions

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