Introduction to Forces

1
Introduction to Forces
2
A force is a push or pull on or by an object.

• The metric unit of force is the newton.
• Many people in the U.S. still use the British
  system and measure force in pounds (lb), ounces
  (oz), and tons.
• 1 N (newton) equals about 1/5 of a pound.

3
Elastic forces are associated with rubber bands,
springs, and other materials that stretch easily
and then return to their original shape.
4
Gravitational force is a force of attraction
between two bodies, even though the bodies are
not touching.

• Gravity depends on the bodies masses and on the
  distance between them.
• Gravitational force is directly proportional to
  the mass of each body.
• The greater the masses, the greater the
  gravitational force between them.
• Gravitational force also depends on the distance
  between objects.

5

• Sir Isaac Newton first described the nature of
  gravitational force.

6
Weight is the measure of gravitational force.

• The units of weight and force are the same,
  newtons.
• To weigh an object, hang it on a spring scale (a
  scale whose stretch is measured with known
  forces.)
• The scale measures the force of gravity on the
  object hanging from the scale.

7
(No Transcript)
8
Mass is related to the amount of matter in an
object.

• The most common metric units of mass are the
  kilogram (kg) and gram (g).
• The British unit for mass is the slug.
• The most common way to measure mass is with a
  balance.

9
(No Transcript)
10

• An objects mass stays the same as it moves from
  place to place but its weight does not.
• A lunar rock moved from the moon to the earth has
  the same mass in both places but weighs six times
  more on the earth because the earths force of
  gravity is six times stronger than the moons.

11
(No Transcript)
12
Mass is measured using a triple beam balance
scale.
13
(No Transcript)
14
(No Transcript)
15
Force, mass, and weight are all important to
understand so we can open the keys of
understanding the world around us.