Glossary
Acceleration
The rate at which an object's velocity changes over time, involving changes in speed, direction, or both.
Example:
When a car speeds up from a stoplight, it experiences positive acceleration.
Acceleration Formula (Atwood Machine)
The derived equation, a = (m2 - m1)g / (m1 + m2), that calculates the acceleration of the masses in an ideal Atwood machine system.
Example:
Using the acceleration formula (Atwood Machine), you can quickly determine how fast two connected blocks will move if you know their masses.
Action-Reaction Pairs
A set of two forces that are equal in magnitude and opposite in direction, acting on two different interacting objects, as described by Newton's Third Law.
Example:
When you push a wall, the wall pushes back on you with an equal and opposite force; these two forces form an action-reaction pair.
Atwood Machine
A system consisting of two masses connected by a string over a pulley, commonly used to demonstrate Newton's Second and Third Laws and analyze forces and acceleration.
Example:
Students often use an Atwood machine in labs to measure the acceleration due to gravity by varying the masses on either side of the pulley.
Force
An interaction that, when unopposed, will change the motion of an object; it is a vector quantity having both magnitude and direction.
Example:
The push you give a shopping cart is a force that causes it to accelerate.
Force Pairs
Another term for action-reaction pairs, emphasizing that forces never occur in isolation but always involve two interacting objects exerting forces on each other.
Example:
The gravitational pull of the Earth on the Moon and the gravitational pull of the Moon on the Earth constitute a set of force pairs.
Free Body Diagram (FBD)
A visual representation of all external forces acting on a single object or system, used to analyze forces and apply Newton's Laws.
Example:
To solve for the tension in a rope holding a hanging mass, the first step is always to draw a free body diagram for the mass, showing gravitational force and tension.
Mass
A measure of an object's inertia, or its resistance to changes in motion, and also a measure of the amount of matter in an object.
Example:
A bowling ball has a much larger mass than a tennis ball, which is why it's harder to accelerate.
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 (ΣF = ma).
Example:
When a car accelerates, the net force from the engine and friction determines its acceleration according to Newton's Second Law.
Newton's Third Law of Motion
For every action, there is an equal and opposite reaction. This fundamental principle states that forces always occur in pairs, acting on two different interacting objects.
Example:
When a rocket expels hot gas downwards, the gas exerts an equal and opposite force upwards on the rocket, propelling it into space. This is an example of Newton's Third Law of Motion.
Simultaneous Forces
Forces in an action-reaction pair that occur at the exact same time; one force does not precede or cause the other.
Example:
When a baseball bat hits a ball, the force of the bat on the ball and the force of the ball on the bat are simultaneous forces, happening at the exact moment of impact.
Tension
The pulling force transmitted axially by means of a string, cable, chain, or similar one-dimensional continuous object, when it is pulled tight by forces acting from opposite ends.
Example:
In an Atwood machine, the string connecting the two masses experiences tension as it is pulled by the weights of the blocks.
Weight
The force of gravity acting on an object's mass, calculated as W = mg, where m is mass and g is the acceleration due to gravity.
Example:
An astronaut's weight on the Moon is less than on Earth because the Moon's gravitational acceleration is smaller.