Glossary
Acceleration
The rate at which an object's velocity changes over time. It can involve a change in speed, direction, or both.
Example:
A car speeding up from a stoplight experiences positive acceleration.
Action-Reaction
A principle from Newton's Third Law stating that for every force (action) exerted by one object on a second, there is an equal and opposite force (reaction) exerted by the second object on the first.
Example:
When a rocket expels hot gas downwards, the gas exerts an equal and opposite action-reaction force upwards on the rocket, propelling it.
Centripetal Force
The net force required to keep an object moving in a circular path, always directed towards the center of the circle. It causes the object to change direction, not speed.
Example:
The tension in a string keeping a ball swinging in a circle acts as the centripetal force.
Circular Motion
The movement of an object along the circumference of a circle or rotation along a circular path. It requires a continuous change in direction.
Example:
A satellite orbiting Earth is an example of circular motion.
Force
A push or pull that can cause an object to accelerate or deform. It is a vector quantity, having both magnitude and direction.
Example:
Kicking a soccer ball applies a force to it, causing it to accelerate from rest.
Free-body diagram
A visual representation used to analyze the forces acting on a single object. All forces are drawn as vectors originating from the object's center of mass.
Example:
Drawing a free-body diagram for a block on an inclined plane helps identify gravitational, normal, and frictional forces.
Inertia
An object's resistance to changes in its motion. It describes the tendency of an object to maintain its current state of motion.
Example:
When a car suddenly brakes, passengers lurch forward due to their inertia resisting the change in motion.
Mass
A measure of the amount of matter in an object and its resistance to acceleration. It is an intrinsic property of an object.
Example:
A bowling ball has significantly more mass than a tennis ball, making it harder to accelerate.
Net Force
The vector sum of all individual forces acting on an object. It determines the object's acceleration according to Newton's Second Law.
Example:
If you push a box with 10 N to the right and a friend pushes with 5 N to the left, the net force on the box is 5 N to the right.
Newton's First Law
States that an object at rest stays at rest, and an object in motion stays in motion with the same velocity unless acted upon by a net external force. It defines inertia.
Example:
A book resting on a table will remain at rest unless a force, like a push or pull, acts on it, illustrating Newton's First Law.
Newton's Laws of Motion
A set of three fundamental laws describing the relationship between a body and the forces acting upon it, and its motion in response to those forces. They form the basis of classical mechanics.
Example:
Understanding Newton's Laws of Motion allows engineers to design safe and efficient vehicles.
Newton's Second Law
States that the net force acting on an object is equal to the product of its mass and acceleration ($F_{net} = ma$). It quantifies the relationship between force, mass, and acceleration.
Example:
Pushing a 10 kg cart with a Newton's Second Law net force of 20 N will cause it to accelerate at 2 m/s².
Newton's Third Law
States that for every action, there is an equal and opposite reaction. Forces always occur in pairs, acting on different objects.
Example:
When you jump, your feet push down on the Earth, and the Earth pushes back up on your feet with an equal and opposite force, demonstrating Newton's Third Law.
SI units
The International System of Units, a standardized system of measurement used in science and engineering. For mechanics, this includes kilograms (kg) for mass, meters (m) for distance, and seconds (s) for time.
Example:
When calculating force using F=ma, always ensure mass is in kilograms, acceleration in meters per second squared, and the resulting force will be in Newtons, which are all SI units.
Velocity
An object's speed in a specific direction. It is a vector quantity.
Example:
A car traveling at 60 mph east has a constant velocity if it maintains that speed and direction.