Glossary
Apparent Weight
The sensation of weight an object experiences, which is determined by the normal force acting on it. It can differ from actual weight when there is vertical acceleration.
Example:
In an elevator accelerating upwards, you feel heavier because your apparent weight increases due to a larger normal force.
Centripetal Acceleration
The acceleration of an object moving in a circular path, always directed towards the center of the circle. It is caused by the change in direction of the tangential velocity.
Example:
When a roller coaster goes through a loop, the riders experience centripetal acceleration directed towards the center of the loop.
Centripetal Force
The net force required to keep an object moving in a circular path, always directed towards the center of the circle. It is not a new type of force but rather the sum of existing forces that cause circular motion.
Example:
The tension in a string keeping a ball swinging in a circle is the centripetal force that prevents the ball from flying off in a straight line.
Contact Forces
Forces that arise from direct physical contact between two objects. Examples include normal force, friction, and tension.
Example:
When you push a box across the floor, the force you exert is a contact force.
Coordinate System
A framework used to define the position and direction of forces and motion, typically consisting of perpendicular axes (e.g., x and y). For circular motion, one axis should point towards the center of the circle.
Example:
When analyzing a car turning a corner, choosing a coordinate system with the x-axis pointing towards the center of the turn simplifies the centripetal force calculation.
Free Body Diagram (FBD)
A visual tool that represents an object as a point mass and shows all external forces acting on it as arrows originating from the point. It helps analyze the object's motion.
Example:
When analyzing a book sliding across a table, drawing an FBD helps visualize the forces of gravity, normal force, and friction.
Friction
A force that opposes relative motion or attempted motion between two surfaces in contact. It can be static (preventing motion) or kinetic (opposing motion).
Example:
When a car brakes, the friction between the tires and the road helps it slow down.
Gravitational Force
A fundamental non-contact force of attraction between any two objects with mass. On Earth, it's the force pulling objects towards the planet's center.
Example:
The gravitational force between the Earth and the Moon keeps the Moon in its orbit.
Newton's Second Law
States that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F_net = ma). It is fundamental to analyzing forces and motion.
Example:
If you push a lighter shopping cart with the same force as a heavier one, Newton's Second Law predicts the lighter cart will accelerate more.
Non-contact Forces
Forces that act on an object without direct physical contact. Examples include gravitational force, electric force, and magnetic force.
Example:
A magnet pulling on a paperclip without touching it demonstrates a non-contact force.
Normal Force (Fn)
The component of a contact force perpendicular to the surface that an object rests on or interacts with. It prevents objects from passing through surfaces.
Example:
When you stand on the floor, the floor exerts an upward normal force on you, preventing you from falling through it.
Tangential Velocity
The instantaneous linear velocity of an object moving in a circular path, always directed tangent to the circle at that point. In uniform circular motion, its magnitude is constant.
Example:
As a car rounds a curve, its tangential velocity is the speed and direction it would travel if it suddenly lost traction and went straight.
Tension
A pulling force transmitted axially through a string, rope, cable, or similar one-dimensional continuous object. It always acts along the length of the string and away from the object.
Example:
When a rock is swung on a string in a vertical circle, the tension in the string changes depending on the rock's position.
Uniform Circular Motion
The movement of an object in a circular path at a constant speed. Although speed is constant, the velocity is continuously changing due to the changing direction, resulting in centripetal acceleration.
Example:
A satellite orbiting Earth at a steady altitude is an example of uniform circular motion, as its speed remains constant while its direction continuously changes.
Weight Force (Fg)
The force of gravity acting on an object, always directed downwards towards the center of the Earth. It is calculated as mass times the acceleration due to gravity (mg).
Example:
A student standing on a scale experiences their weight force pulling them downwards, which the scale measures.