Objectives Types of Forces Freebody Diagrams Net Force
Objectives • Types of Forces • Free-body Diagrams • Net Force
Do Now Forces can be broken into 2 main categories which you read about for homework. What are they?
Types of Forces Contact Field Normal Friction Applied Spring Air resistance Tension Magnetic Electric Gravity
• Applied Force (Fa) - An applied force is a push or pull acting on an object by another object or person. • Normal Force (FN) - the support force exerted upon an object which is in contact with another stable object. – Directed perpendicularly to the support surface.
• Frictional Force (Ff) - force exerted by a surface as an object moves across it or makes an effort to move across it. – Rough surface more friction – The result of molecules from each object creating instantaneous bonds with each other.
Mass vs Weight • Mass (m) – the amount of matter in an object. – SI unit is kilograms (kg) – Is the same at every location. • Gravitational Force (Fg) - the force with which the earth, moon, or other massive body attracts an object towards itself. This is the weight of an object. – Varies depending upon location, mass, acceleration due to gravity. – Fg = mg
Free-body Diagrams -represents object as a point particle with all forces acting on it drawn as vectors.
An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces acting on the egg as it falls.
A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance. Diagram the forces acting on the squirrel.
Carl pushes a box horizontally across the carpet accelerating it to the right. Consider friction. Diagram the forces acting on the box.
A football is moving upwards towards its peak after having been booted by the punter. Neglect air resistance. Diagram the forces acting upon the football as it rises upward towards its peak.
A car is coasting to the right and slowing down. Diagram the forces acting upon the car.
Net Force • To find the net force acting on an object: – Write down x forces and y forces including +/– Add all x forces then all y forces – Add the x forces and y forces using Pythagorean Theorem – Find the angle of the net force using inverse tangent
Fnet=17 N right Net Force FN=30 N Ff=9 N Fa=26 N Fg=30 N
Fnet=15. 3 N at 78. 7 degrees down from the force of the wind Net Force Fwind=3 N Fg=15 N
Fnet=20. 4 N at 11. 3 degrees down from the applied force Net Force FN=16 N Ff=10 N Fa=30 N Fg=20 N
Find force D and E
Ff = 3 N Net Force = 9. 5 N at 18. 4° above Fa FN=7 N Fa=12 N Ff = ? Fg=4 N
- Slides: 18