# Forces: Maintaining Equilibriumor Changing Motion

Objectives:
• Define force
• Classify forces
• Define friction force
• Define weight
• Determine the resultant of two or more forces
• Resolve a force into component forces acting at right angles to each otherbrea
• Determine whether an object is in static equilibrium, if the forces acting on the object are known
• Detemine an unknown force acting on an object, if all the other forces acting on the object are known and the object is in static equilbrium

A force is a push or a pull.
A force is something that has the ability to accelerate an object.

Forces are described in units of Newtons or pounds
1N = 0.225lb
1lb = 4.45N
How much do you weigh?

Internal forces-Forces that act within the object or system whose motion is being investigated.

External forces-Forces that act on an object as a result of its interaction with the environment surrounding it.

Friction
Static and dynamic friction

F=μN

Normal force and surface area (book examples)

If a runner exerts a vertical force of 2000 N, and the coefficient of static friction between the shoe and the ground is 0.50, what is the maximum horizontal force he can generate under his shoe?

W=mg

What happens when there is more than one force?

Vectors involve magnitude and direction

Combining Vectors: Graphical and Additive Methods

Field experience (Ground reaction forces in running)

Trigonometry Aaahhhhhh!!!!!

Pythagorean Theorum

Real-life situation

Static Equilibrium
 When an object is at rest and the forces acting on the object are in equilibrium, they result in a net force of zero. Weightlifter example: Person's mass=80kg, barbell=70kg, ground reaction force=1470N. Is this system in static equilibrium? Twister! Gymnast