Overview
This lesson explains the concept of resultant force, how to calculate it for forces in a straight line, and how to represent forces on an object using Freebody diagrams.
Resultant Force Concept
- A force is a push or pull on an object due to interaction with another object.
- Forces are vector quantities, meaning they have both magnitude (size) and direction.
- The resultant force is a single force that has the same effect as all original forces acting together.
- To find the resultant force, subtract the smaller force from the larger force, considering direction.
Calculating Resultant Forces in a Straight Line
- Example: If a man pushes a box with 20 N right and friction opposes with 10 N left, the resultant is 10 N right.
- For multiple forces on a car: Add forces acting in the same direction and then subtract from forces in the opposite direction.
- Driving force 10,000 N left, friction 4,000 N right, air resistance 5,000 N right.
- Total rightward force: 4,000 N + 5,000 N = 9,000 N.
- Resultant force: 10,000 N (left) - 9,000 N (right) = 1,000 N left.
Balanced Forces and Zero Resultant Force
- When upward and downward (or left and right) forces are equal, the resultant force is zero.
- Example: Skydiver with 800 N weight down and 800 N air resistance up experiences balanced forces (resultant force = 0).
Freebody Diagrams
- Freebody diagrams represent all forces acting on an object as arrows from a point.
- Arrow length shows force magnitude; arrow direction shows force direction.
- Example: Airplane at constant altitude and velocity
- Weight acts downward; lift acts upward with equal magnitude.
- Thrust (forward force) and drag (air resistance, backward force) are equal at constant velocity.
- Balanced arrows indicate zero resultant force in both vertical and horizontal directions.
Key Terms & Definitions
- Force — A push or pull acting on an object due to interaction with another object.
- Vector quantity — A quantity that has both size (magnitude) and direction.
- Resultant force — The single force that has the same effect as all other forces acting together.
- Freebody diagram — A diagram showing all the forces acting on an object represented as arrows from a point.
- Thrust — The forward force provided by an airplane's engines.
- Lift — The upward force acting against weight for an airplane.
- Drag (air resistance) — The force acting opposite to the direction of motion through air.
Action Items / Next Steps
- Practice drawing Freebody diagrams for different objects.
- Solve problems calculating resultant forces from various scenarios.
- Review workbook questions on resultant forces if available.