Force & Motion Part 2 Mrs. Wright. LET’S REVIEW… Force: A push of pull applied to an object...
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Transcript of Force & Motion Part 2 Mrs. Wright. LET’S REVIEW… Force: A push of pull applied to an object...
Force & Motion Part 2
Mrs. Wright
LET’S REVIEW…
Force: A push of pull applied to an object
Friction: The force that one surface exerts on another when the two surfaces rub against each other.
FRICTION
Friction is caused by microscopic bumps on surfaces called: MICROWELDS
The picture on the right is of Aluminum Foil at 10,000X magnification.
Friction Is Very Useful…
Friction keeps our feet from sliding out from under us when we are walking
Friction keeps our shoelaces tied
Friction gives us the ability to open a round door knob.
Can you think of others things it would be hard to do without friction?
FRICTION
Depends On 3 Things
How hard the surfaces push together
The surface areas in contact with each other
Types of surfaces involved
Example of Friction
Sled moving across the snow
The bottom of the sled rubs against the snow
Fireman sliding down the pole
The skin of his hands rub against the polished metal
4 Types of Friction
Static Friction
The friction that acts on objects that are not moving
Initial friction when moving an object
Example
4 Types of Friction
Sliding Friction
Occurs when two solid surfaces slider over each other.
Example
4 Types of Friction
Sliding Friction
Occurs when two solid surfaces slider over each other.
Example
Rolling Friction
When an object rolls across a surface
4 Types of Friction
Fluid Friction
Occurs when a solid object moves through a fluid
Fluid – a material that FLOWS
Water
Oil
AIR
Example
How well were you listening?
STAND UP…
What are the four types
of friction?
Can you show me an
example of sliding friction?
Give me a new example of
rolling friction.
Give me a new example of
fluid friction
Another Type of Force…
GRAVITY
A force that PULLS objects toward each other
People all around the planet are being pulled toward the surface of the Earth.
Gravity pulls everything toward the Earth’s surface at a rate of 9.8m/s2
WEIGHT VS. MASS
Mass: the measure of the amount of matter in an object, measured in grams on a balance
Weight: A measure of the gravitational force exerted on an object BECAUSE of its mass
WEIGHT = Mass (kg) X Gravity (9.8m/s2)
100kg X 9.8m/s2
WEIGHT = 980N
WEIGHT VS. MASS
FORCES
The strength of a force is measured in the SI unit called the NEWTON (N).
You exert about 1N of force when you lift a small lemon
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 longer the arrow, the greater the force.
FORCES
NET FORCES
The combination of ALL forces acting on an object
The net force determines whether
An object moves & what direction it moves in
Combining Forces
When forces act in the same direction, the net force can be found by ADDING the strengths of the individual forces
Combining Forces
When forces act in opposite directions, they also combine to produce a net force, HOWEVER, you must pay attention to the direction of the each force.
When two forces act in opposite directions, they combine by SUBTRACTION
UNBALANCED FORCES
Unbalanced forces can cause an object to start moving, stop moving, OR change direction.
Unbalanced forces acting on an object result in a net force and cause a change in the object’s direction
Tug of War
Balanced Forces
Equal forces acting on one object in opposite directions are called balanced forces
Balanced forces acting on an object DO NOT change the object’s motion
Time To Stand Up
Again…
Explain Unbalanced
Forces
Give a new example of
an unbalanced force
Explain Balanced Forces
Give a new example of a
balanced force