Transcript FORCES - Mr. Maloney

FORCES
episode I
Newton’s hope
Physics
Mr. Maloney
Objectives
You will be able to …
 understand the idea of force
 categorize forces into the two main types
of force
 recognize when forces exist
 use Newton’s 3rd Law to describe how
objects interact with each other.
Forces
So far we worked on observing
and describing motion
Our next goal will be to figure
out what causes motion to
change or not change.
How do objects interact?
Dragging
things
Punching a Wall
Hitting in football or Hockey
Jumping in dancing or skating
Tossing in cheerleading
A push or a pull
What is a Force?
A
push or pull
 Forces are the way objects interact.
 This interaction can cause the objects’
motion to change (acceleration), or it
could cause nothing at all depending
on the circumstances and how many
objects are interacting.
What is a Force
 Forces
are VECTOR quantities
 They have a magnitude (SIZE) and a
direction
Types of forces
There
are two types of forces
Contact Forces
At a distance forces
Contact Force
 Forces
for which the two
interacting objects have to be
physically in contact with each other
for the forces to exist.
 EXAMPLES
 Hitting
 Pulling
with a rope
 Lifting weights
 Pushing a couch
 Lying on a table
 Poking
someone
 Sliding to block a
kick
 Hanging from a
window ledge
At A Distance Force
 Forces
in which the two interacting
objects are not in physical contact with
each other, but are still able to exert a
push or pull and interact with each
other despite the physical separation.
 Know
any?
Examples of Forces

Contact







Friction Force (Ff, f)
Tension (FT, T)
Normal Force (FN, N)
Air Resistance (Fair)
Applied Force (Fa, F#)
Spring Force (Fsp)
At a Distance




Gravitational Force (Fg)
Electrical Force (FE)
Magnetic Force (FM)
Nuclear Forces
An Aside …
4 Fundamental Forces
We will use a large number of forces, but there are
actually only four different kinds of forces
in the universe:
1. The gravitational force - how objects with mass
interact with one another
2. The electromagnetic force - how charged objects
interact with one another (all contact forces can
be traced to electromagnetic interactions)
3. The strong nuclear force - holds nuclei together
4. The weak nuclear force - associated with
radioactivity
Newton’s Laws
 In
the 1600’s, Isaac Newton established 3
laws of motion which described the
relationship between motion and Force.
 For this chapter’s project, create a
MultiMedia presentation on Isaac Newton’s
Laws….
 Recreate examples demonstrating his 3
laws of motion and his law of gravity.
 Lets See some from other years!
How things interact (ILD 2.1)
 When
you hit a wall with your fist what
happens?
 When a bug splats on your windshield what
happens?
 How about when you push a couch across
a floor?
 How do you interact with these objects …
how do they interact with you?
Results of ILD 2.1
A bug splats on your windsheild as you are
driving. What feels a bigger force?
A) The bug does
B) The windshield does
C) They feel the same force
D) Neither feel any force
Newton’s 3rd Law

For every action there is an equal
and opposite reaction
 Forces always occur in equal magnitude and
opposite direction pairs.
 Forces only exist during interactions.
 One of the pair forces acts on one object, and
the other pair force acts on the other object
 The 3rd law is often called the law of actionreaction (even though I don’t like it)
Newton’s 3rd Law
 Why
are people so often tricked. Why
do we think the bug feels a greater force
than the windshield, when in reality they
feel the same?
 Although the forces are the same the
effect of the force on each object is
different. That force on the bug squishes
it, but the same force on your windshield
only gives you something to clean.
Newtons 3rd Law Examples
Take a few minutes and write down how you think
Newton’s 3rd law applies to these situations.
Describe what objects are interacting, and what is
the effect of these interactions.
 You are swimming thru a pool of water
 Car driving on flat ground
 A gun shoots a bullet and recoils
 Punching a wall or paper
 You jump out a window and fall to the ground
 Bart and the fire extinguisher
Objectives summary
Do you…
Understand the idea of force
 Forces
are vector pushes or pulls which
have a magnitude and direction
Be able to Categorize forces into the two main types of force
 Contact
and At a Distance Forces
Be able to Recognize when forces exist
 Forces
only exist during interactions
between objects
Be able to use Newton’s 3rd Law to describe how objects interact.
 Forces
occur during interactions and are
equal in size on each object but opposite
in direction.
Newtons 3rd Law Examples
Identify at least 6 pairs of 3rd Law forces in the
situation below …