Objectives:
Force and Motion
Forces between objects act when the objects
are in direct contact or when they are not
touching.
Magnetic, electrical and
gravitational forces can act at a
distance.
(Contact vs. noncontact forces)
Notes: Force
Force
The capacity to do work or cause physical change;
energy, strength, or active power.
Measured in units of Newtons or N
What forces do you notice in this “moving” car?
Contact vs. Noncontact Forces
Contact Forces
•
▫
Force applied to an object by another body that is in contact with it.
▫
Air Resistance
▫
Friction
Noncontact Forces
•
Force applied to an object by another body that is not in contact
with it.
▫
▫
Electromagnetism
Gravity (Weight)
▫
Net Force = the overall force acting on
an object
1
Example 1:
Net force =
Example 2:
Net force =
2
3
Example 3:
Net force =
Example 4:
Net force =
4
Example 5:
Net force =
14 N
10 N
6N
A field model - explains how two objects
can exert forces on each other without
touching.
Field - a region of influence surrounding an object.
•When a second object with an appropriate property
is placed in this region,
•the field exerts a force
•can change the motion of the object.
Examples of Fields
•1. Electric
•2. Magnetic
•3. Gravitational
Electric fields - exist around objects
with charged particles.

When a second object with charge is placed in the
field:

the two objects experience electric forces that
can attract or repel them
Electric force weakens rapidly with increasing
distance.
Magnetic fields - exist around
magnetic objects.
When a second magnetic object is placed in the
field:
the two objects experience magnetic
forces that attract or repel them.

Magnetic force weakens rapidly with
increasing distance.
Magnetic field lines can be seen when
iron filings are sprinkled around a
magnet.
Gravitational fields - exist around objects
with mass.
When a second object with mass is placed in the field,
the two objects experience attractive
gravitational forces toward each other.

•Gravitational force weakens rapidly with
increasing distance.
•Every object exerts a gravitational force
on every other object with mass.
•
Gravitational force:
•
Forces are hard to detect unless at least
one of the objects is very massive
•
•
•
Examples: sun and planets
increases with the mass of the objects
points toward the center of objects.
•Weight is gravitational force and is often confused
with mass.
•Weight is proportional to mass, but depends
upon the gravitational field at a particular
location.
•.
Weight and Gravity
An object will have the same mass when it is on
the moon as it does on Earth.
Weight (force of gravity) will be different at these
two locations.
Notes: Electricity and Magnetism
Electricity is related to magnetism.
-Magnetic fields can produce electrical currents in
conductors.
-Electric currents produce magnetic fields.
Electromagnets
Electromagnets - temporary magnets that lose
their magnetism when the electric current is
turned off.
Used in electric motors, generators, loudspeakers,
doorbells, and many other uses
Video Clips
SciShow – Electricity
https://www.youtube.com/watch?v=GMnsZuEE_m8
SciShow – Magnets
https://www.youtube.com/watch?v=cy6kba3A8vY
Generators
Generators - convert mechanical energy into
electrical energy
- are used to cause electrical energy to flow in
power plants.
Electric motors
Electric Motors - Convert electrical energy into
mechanical energy.
• Motors are in blenders and washing machines.
•
Both motors and generators have magnets and a coil of
wire that creates its own magnetic field when an
electric current flows through it.
There is a difference between magnetic
poles and electric charges.
2 magnetic poles = NORTH &
SOUTH
2 electric charges = POSITIVE &
NEGATIVE