1. Friction and Applied Force:
* Friction: This force opposes motion and acts between surfaces in contact. Its magnitude depends on the materials involved and the force pressing the surfaces together.
* Applied Force: This is a force directly applied to an object, like pushing a box.
* Example: Imagine pushing a heavy box across a rough floor. You apply a force to move it, but friction acts in the opposite direction, resisting your push. The applied force needs to be greater than the friction force to make the box move.
2. Gravity and Air Resistance:
* Gravity: The force pulling objects towards the center of the Earth. It's relatively constant near the Earth's surface.
* Air Resistance: A force that opposes the motion of objects through the air. It depends on the object's speed, shape, and the density of the air.
* Example: Think of a parachutist. Gravity pulls them down, but air resistance increases as they fall, eventually balancing the force of gravity and allowing them to reach a terminal velocity.
Key Concept: When forces are not equal, the object they act upon will accelerate in the direction of the larger force.
