Different Types of Forces

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Different Types of Forces

• Gravity (also called weight)
• Friction
• Applied Force
• Air Resistance
• Tension
• Spring Force
• Normal Force (also called support force)
• http//www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/n
  ewtlaws/u2l2b.htmlspring

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2.3 Definition of Forces

• Force of attraction due to mass of an object
• Pulled force applied to a rope, wire or cable
• Elastic, compressed or stretched force
• Any push or pull on an object
• Resistance of two objects in contact moving past
  each other
• Resistance of an object moving through the
  atmosphere
• Force that pushes back on one object resting on
  another

• Gravity
• Tension Force
• Spring Force
• Applied Force
• Friction
• Air Resistance
• Normal force

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2.3 Support Force

• For an object at rest on a horizontal surface,
  the support force (normal force) must equal the
  objects weight (gravity).

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2.1 Force

• Tension, Weight and Spring

The upward tension in the string has the same
magnitude as the weight of the bag, so the net
force on the bag is zero. The bag of sugar is
attracted to Earth with a gravitational force of
2 pounds or 9 newtons.
Spring force (in scale)
Tension (in string)

• 1 lb 4.45 N

Weight (of bag)

• 9 N of weight 9 N of tension and spring force

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2.3 Support Force
Support Force (also called normal force)
The table pushes up on the book with as much
force as the downward weight of the book.
Fnorm Fgrav
Net force
Weight (also called gravity)
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2.3 Support Force Physics
The book lying on the table compresses atoms in
the table and they squeeze upward on the book.
The compressed atoms produce the support force.
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2.3 Support Force
The upward support force is as much as the
downward pull of gravity.
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2.3 Support Force
The upward support force is as much as the
downward pull of gravity.
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2.3 Support Force

• think!
• What is the net force on a bathroom scale when a
  110-pound person stands on it?

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2.3 Support Force

• think!
• What is the net force on a bathroom scale when a
  110-pound person stands on it?
• Answer Zerothe scale is at rest. The scale
  reads the support force, not the net force.

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2.3 Support Force

• think!
• Suppose you stand on two bathroom scales with
  your weight evenly distributed between the two
  scales. What is the reading on each of the
  scales? What happens when you stand with more of
  your weight on one foot than the other?

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2.3 Support Force

• think!
• Suppose you stand on two bathroom scales with
  your weight evenly distributed between the two
  scales. What is the reading on each of the
  scales? What happens when you stand with more of
  your weight on one foot than the other?
• Answer In the first case, the reading on each
  scale is half your weight. In the second case, if
  you lean more on one scale than the other, more
  than half your weight will be read on that scale
  but less than half on the other. The total
  support force adds up to your weight.

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2.3 Support Force
For an object at rest on a horizontal surface,
what is the support force (or normal force) equal
to?

• The objects weight (or gravity)!

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2.1 Force

• Tension and Weight

A stretched spring is under a stretching force
called tension. Pounds and newtons are units of
weight, which are also units of force. Weight is
a force.