- 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.
Static and dynamic friction
Static friction: The force occurring between two dry surfaces that are not moving relative to each other.
Dynamic friction: The force occurring between two dry surfaces that are moving relative to each other.
Static followed by dynamic friction
Shoe friction in running
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?
Addition of Forces
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)
A 70 kg runner experiences a 6 m/s headwind causing air resistance of 15 N. During the heelstrike, he exerts an A/P force of 100 N. The vertical force at this time was 1300 N.
Draw a free body diagram of this situation and determine the resultant force (magnitude and direction).
|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?