Seeing forces (sunday)
1. What is a Force?
A force is a push or a pull acting upon an object resulting from the object's interaction with another object.
While you cannot physically "see" a force itself with your eyes, you can see what it does. Forces cause changes in an object's:
Speed: Speeding up (acceleration) or slowing down (deceleration).
Direction: Changing the path of a moving object.
Shape: Stretching, compressing, bending, or twisting.
2. Representing Forces: Force Diagrams
Because forces have both a size (magnitude) and a specific direction, they are vector quantities. We "see" them on paper using arrows.
Free-Body Diagrams (FBDs)
A free-body diagram models the object as a simple box or dot and shows all the external forces acting on that object.
The Arrow's Direction: Shows the direction of the force.
The Arrow's Length: Represents the magnitude (strength) of the force. A longer arrow means a stronger force.
The Label: Identifies the type of force.
3. Types of Forces to "Look For"
When analyzing a scenario, forces are generally split into two categories:
Contact Forces (Objects must touch)
Friction : Opposes motion; acts parallel to the surface.
Normal Force: The upward support force exerted by a stable surface perpendicular to the object resting on it.
Tension: The pulling force transmitted through a string, rope, or cable.
Air Resistance: A type of friction caused by air particles hitting a moving object.
Non-Contact Forces (Action at a distance)
Gravitational Force: The pull toward the center of a massive body (like Earth). Also known as weight.
Magnetic Force: Attraction or repulsion between magnetic poles.
Electrostatic Force: Attraction or repulsion between electrical charges.4. How We Measure Forces
The Unit: Forces are measured in Newtons (N). One Newton is the force required to accelerate a 1 kg mass at a rate of
The Instrument: We use a force meter (also called a Newtonmeter or spring balance). It works based on Hooke’s Law, which states that the extension of a spring is directly proportional to the force applied to it.