unit 2 forces and motion mechanical equilibrium · ch. 2 mechanical equilibrium.notebook october...
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Ch. 2 Mechanical Equilibrium.notebook October 11, 2011
Unit 2 Forces and Motion Mechanical Equilibrium
• Force: a push or a pull that acts on an object
Things that are in balance with one another illustrate equilibrium.
A force is needed to change an object’s state of motion.
The scientific unit of force is the newton, abbreviated N
Ch. 2 Mechanical Equilibrium.notebook October 11, 2011
Net Force• Net Force: the overall force acting on an object after all the forces are combined• Equilibrium/Balanced Forces: when the forces on an object are balanced, the net force is zero and there is no change in the object’s motion.• Unbalanced forces: When an unbalanced force acts on an object, the object accelerates.• Tension: force in a rope when pulled or streched• Ex. Book on your desk? What’s happening?• Ex. Weights on a spring scale?
Ch. 2 Mechanical Equilibrium.notebook October 11, 2011
Net ForceThe net force depends on the magnitudes and directions of the applied forces.
Ch. 2 Mechanical Equilibrium.notebook October 11, 2011
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.
• tension force acting upward • weight acting downward
Ch. 2 Mechanical Equilibrium.notebook October 11, 2011
Mechanical equilibrium is a state wherein no physical changes occur. Whenever the net force on an object is zero, the object is in mechanical equilibrium—this is known as the equilibrium rule.
Note the readings on the scales. Burlthe painter has a weight of 600 N,and carries a 100N bucket of paint.What is the weight of the scaffold?
Ch. 2 Mechanical Equilibrium.notebook October 11, 2011
Net Force- Equilibrium
The upward force that balances the weight of an object on a surface is called the support force. A support force is often called the normal force.
think!What is the net force on a bathroom scale when a 110pound person stands on it?
Equilibrium for Moving Objects
Ch. 2 Mechanical Equilibrium.notebook October 11, 2011
A vector is an arrow that represents the magnitude and direction of a quantity. A vector quantity needs both magnitude and direction for a complete description. Force is an example of a vector quantity.A scalar quantity can be described by magnitude only and has no direction. Time, area, and volume are scalar quantities.
The sum of two or more vectors is called their resultant. Combining vectors is quite simple when they are parallel:• If they are in the same direction, they add. • If they are in opposite directions, they subtract.
Ch. 2 Mechanical Equilibrium.notebook October 11, 2011
Vector vs. Scalar
represent vectors w/arrows
10 m/s
10 m/s