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Physics Forces - 8th Grade

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William Begoyan

on 16 March 2016

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Transcript of Physics Forces - 8th Grade

The Physics of Forces
Page 41 in your ISN
- Pages 374-400 in the Textbook

By: Mr. Begoyan
What is a
force
?

A
force
is a push or a pull.
A
force
has magnitude, and a direction in which it acts.
Force
is a vector
The combination of all the forces acting on an object is called the
net force.
Engine power
Friction
Gravity
Air Pressure
Wind
Balanced forces
result in no net force, with no change in the object's velocity.
Unbalanced forces
result in a net force, causing a change in the object's velocity.
Friction
,
Gravity
, and
Elastic Force

300-300 = 0
400-300 = 100
100 N
Friction
is a force created when 2 surfaces rub against each other.
Friction
always acts in the opposite direction to the motion of the object.
Pushing Force
Friction
Motion
The strength of friction depends on the
types of surfaces
involved, and
how hard
they are
pressed together
.
There are 4 types of friction forces:
Static friction
acts on objects that are not moving.
It must be overcome for a n object to start moving.
Rotor Motion
Brake Pad Friction
Sliding friction
occurs when 2 solid surfaces slide over each other.
Motion
Sliding friction
When an object rolls across a surface,
rolling friction
occurs.
Rolling friction
is less powerful than sliding friction.
Motion
Rolling Friction
Fluid friction
occurs when a solid object moves through a fluid.
Fluid friction
Gravity
is a force that pulls objects towards each other.
All objects exert
gravity
.
Isaac Newton
was the first to notice this force.
As distance between objects increases, gravity decreases.
As mass of the objects increases, gravity increases.
Force is measured in newtons (N)
1 N = 1 kg * m/s
2
Gravitational forces exerted on an object's mass are known as
weight.
Weight
will vary with the force of gravity.
Weight
=
Mass
*
Acceleration from gravity
.
Bathroom scales measure your force, then convert it to your "mass" by accounting for Earth's gravity.
When you go to the Moon, this scale will not work as it is not calibrated for the Moon's gravity.
Calculate your actual weight (force) by multiplying your mass by 9.8 m/s
Hint: 1kg=2.2lb

2
When gravity is the only force acting on an object, the object is in
free fall.
Objects that are thrown and experience gravity are called
projectiles.
Force
Gravity
Projectile path
Elastic matter
will return to its original form after being squeezed or stretched.
As you
stretch
or
compress
an elastic material, it exerts a counter force in the opposite direction.
This is called
elastic force
.
Acceleration from gravity
= 9.8 m/s
2
Static Friction
Newton's Laws of Motion
Questions part 1
1. What is a force, and what is force described as?
2. What is a net force? What are the 2 possible outcomes of a net force?
3. What is force measured in?
4. What is friction? What are the different types of friction?
5. What is gravity, and how is it calculated?
6. What is free fall and projectile motion?
Newton's First Law of Motion:
Objects tend to resist changes in motion unless an unbalanced force acts on them.
I am not going anywhere unless someone forces me to!
I'll keep going until something stops me!!
The object's tendency to resist changes in motion is called
inertia
.
Newton's Second Law of Motion:
Acceleration depends on the net force acting on the object and the object's mass.
Force = mass * Acceleration
Newton's Third Law of Motion:
If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object.
Momentum is a quantity of motion.
Momentum = Mass * Velocity
Momentum is a vector
The total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision.
This is the
law of conservation of momentum.
10 km/h
0 km/h
5 km/h
5 km/h
Questions part 2
7. What is elastic force?
8. What does Newtons 1st Law of Motion state?
9. What is inertia?
10. What does Newtons 2nd Law of Motion state?
11. What does Newtons 3rd Law of Motion state?
12. What is momentum?
On page 40, describe the following terms to a 5th grade audience (use words and visuals):

Force, Gravity, Friction
Full transcript