Chapter 2 - Forces
Lesson 1 – The Nature of Force
Vocabulary
•Force:
a push or pull
•Newton (N): SI unit for force
•Named
after Sir Isaac Newton
•Force
is described by it’s strength and
by the direction in which it acts
Force is going to the right.
The force moving to the
right is stronger then the
force moving to the left.
Force is going to the left.
How do forces affect
Motion?

Unbalanced Forces

Balanced Forces
A nonzero net force causes a change in the object’s motion.
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
http://webpath.follettsoftware.com/resource/viewur
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Chapter 2 - Forces
Lesson 2 – Friction and Gravity
Friction
The force that two surfaces exert on each other when
they rub against each other
What affects Friction?
1. Type of surface
2. How hard the surfaces are pushed together.
In general, smooth surfaces create less friction than rough surfaces and
friction increases when surfaces push harder against each other.
Types of Friction
Includes
Air
More examples:

Static Friction

Sliding Friction

Fluid friction

Rolling Friction
What affects Gravity?
Gravity is the force that pulls objects toward each other.
•
Acts everywhere in the universe, not just Earth
Law of Universal Gravitation – States that the force of gravity acts
between all objects in the universe that have mass.
Two Factors that affect gravitational attraction between
objects – mass and distance
Factors affecting Gravity
continued…
Mass (kg) – the amount of matter in an object.
The more mass an object has, the greater gravitational force between it and other
objects.
Gravitational forces is small between
objects with small masses.
Gravitational force is larger between
Objects with larger masses.
As distance increases, gravitational forces decreases.
Elephant vs. Cat

Elephant – has more mass

Cat – Has less mass
The amount of gravity between the Elephant
and Earth is greater than the amount of
gravity between a cat and Earth – That’s why
we can pick up a cat!
Weight vs. Mass

Weight is the force of Gravity on
an object.