Transcript Agents Carry Force Two Types - Red Hook Central School District

Types of Forces
Four Main Forces in Universe
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Gravity Fg.
Electromagnetic EM
Strong Nuclear Strong or Nuclear
Weak Nuclear Weak
•All Forces fall into one of the above
categories.
Common Forces
Weight Fg = mg
gravity interaction with mass.
Weight depends on gravity,
Mass does not.
What is mass?
Amount of matter in object.
• Normal Force
(reaction force) –
• perpendicular to
the surfaces in
contact.
• Opposite to weight
on horizontal
surface.
• Fn = -W
What if you’re leaning on a wall.
Where is the normal force?
Where is it now?
Sliding Friction – force acts at contact between
surfaces. Direction of friction opposes velocity
or attempted velocity.
Which way is friction?
Ff = mFn
m is constant
Which way is the book moving?
Right
Left
The box is not moving.
• Tension –
• transmitted through string, rope, or
wire by forces at each end.
Air Resistance – air friction.
Big reason for bad fuel economy in
cars.
Spring or Elastic Force –
Force applied by stretched
or compressed spring
described by Hooke’s Law.
Magnetic Force
Electrical
Force is a vector quantity. It has
direction.
Acceleration – Dv – is always in
the same direction as the net
force!!
Free Body Diagrams
• Diagrams to show
relative magnitude &
direction of all vector
forces acting on a body.
• Sizes of arrows show
magnitude of force.
• Arrowhead shows
direction of forces.
What can you say for sure about the object
in the free body diagram below?
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1. It is at rest.
2. It is in motion to the left.
3. It is in motion to the right
4. Not enough information to know.
Balanced & Unbalanced Forces
An unbalanced force is a resultant or net force.
What is the Fnet?
What can you say about the motion?
12 N
4N
Fnet = - 8 N or 8 N left
The object shows Acceleration left.
A bird flies with a constant velocity to
the left at a constant altitude. What is
the free body diagram?
V = 0 up so no Fnet up. F bird cancels Fgrav.
Const v horiz. So no Fnet left. Friction
balanced by force of bird left.
F bird up
F bird left
F air fric
F grav
Assignment
• Handout “Free Body
Diagrams”
Number One
Number Two
Number Three
Number Four