Glossary
Balanced Forces
Forces acting on an object that sum to zero, resulting in no change in the object's velocity (i.e., translational equilibrium).
Example:
When you push a heavy box but it doesn't move, the friction force is providing balanced forces against your push.
Balanced Forces
Forces acting on an object that are equal in magnitude and opposite in direction, resulting in a net force of zero.
Example:
A book resting on a table experiences balanced forces: the downward gravitational force is equal and opposite to the upward normal force from the table.
Components
The parts of a vector that lie along perpendicular axes (typically x and y), used to simplify vector addition and analysis.
Example:
To analyze a force pulling a sled at an angle, you break it down into horizontal and vertical components.
Constant Velocity
Motion at a steady speed in a straight line, indicating that the object is not accelerating and the net force acting on it is zero.
Example:
A car cruising on a highway at 60 mph without changing lanes is moving at a constant velocity.
Direction
The orientation or path along which a vector quantity acts.
Example:
When describing wind, you need both its speed (magnitude) and its direction (e.g., blowing north).
Dynamic Equilibrium
A specific type of translational equilibrium where an object is moving at a constant velocity (constant speed and constant direction) because the net force acting on it is zero.
Example:
A skydiver falling at terminal velocity is in dynamic equilibrium because the drag force balances gravity.
Fictitious Forces
Apparent forces that arise in non-inertial reference frames, used to explain observed accelerations within that frame.
Example:
The 'force' that pushes you to the side when a car turns sharply is a fictitious force (like the centrifugal force) experienced in the car's accelerating frame.
Free-body Diagram
A visual representation of an object, showing all external forces acting on it as vectors originating from the object's center.
Example:
Before solving a problem involving a block on an inclined plane, drawing a free-body diagram helps identify and visualize the gravitational, normal, and frictional forces.
Inertia
The property of an object that resists changes in its state of motion; directly proportional to an object's mass.
Example:
It's much harder to push a heavy shopping cart than an empty one because the heavy cart has more inertia.
Inertial Reference Frame
A reference frame in which Newton's first law of motion holds true; it is either at rest or moving at a constant velocity.
Example:
A physics experiment conducted in a laboratory that is stationary relative to the Earth is typically performed in an inertial reference frame.
Inertial Reference Frame
A non-accelerating reference frame in which Newton's First Law of motion holds true, meaning objects with no net force maintain constant velocity.
Example:
For most physics problems, a laboratory fixed to the Earth's surface is considered an inertial reference frame.
Law of Inertia
Another name for Newton's First Law, emphasizing an object's resistance to changes in its state of motion.
Example:
A hockey puck sliding across a frictionless ice rink will continue at a constant velocity because of the law of inertia.
Law of Inertia
Another name for Newton's First Law, emphasizing an object's inherent resistance to changes in its state of motion.
Example:
When a car suddenly brakes, your body continues to move forward due to its law of inertia, resisting the change in motion.
Magnitude
The size or amount of a vector quantity, without regard to its direction.
Example:
The speedometer in your car tells you the magnitude of your velocity, but not the direction.
Net Force
The vector sum of all individual forces acting on an object. It determines whether an object will accelerate or remain in equilibrium.
Example:
If you push a box with 10 N of force and a friend pushes it in the opposite direction with 8 N, the net force on the box is 2 N in your direction.
Net Force
The total vector sum of all individual forces acting on an object, determining its acceleration or lack thereof.
Example:
If two people push a box with 10 N each in the same direction, the net force on the box is 20 N in that direction.
Newton's First Law
Also known as the law of inertia, it states that an object will maintain its state of motion (either at rest or moving at a constant velocity) unless acted upon by a net force.
Example:
When a car suddenly brakes, your body continues to move forward due to Newton's First Law.
Newton's First Law
A fundamental principle stating that an object will maintain its state of motion (at rest or constant velocity) unless acted upon by a net external force.
Example:
A spaceship drifting through space at a constant speed will continue to do so indefinitely, even with its engines off, because there is no net external force acting on it.
Non-Inertial Reference Frame
A reference frame that is accelerating, where Newton's first law does not directly apply without introducing fictitious forces.
Example:
Inside a car that is rapidly accelerating from a stop, you feel pushed back into your seat, indicating you are in a non-inertial reference frame.
Static Equilibrium
A specific type of translational equilibrium where an object is at rest and remains at rest because the net force acting on it is zero.
Example:
A bridge standing perfectly still, supporting its own weight and traffic, is in static equilibrium.
Translational Equilibrium
The state where the vector sum of all forces acting on an object is zero, resulting in no acceleration and thus constant velocity (which includes being at rest).
Example:
A hot air balloon hovering perfectly still in the sky is in translational equilibrium because the buoyant force balances gravity.
Translational Equilibrium
A state where the net force on an object is zero, meaning the object is either at rest or moving at a constant velocity.
Example:
A skydiver falling at terminal velocity is in translational equilibrium because the upward air resistance perfectly balances the downward gravitational force.
Unbalanced Forces
Forces acting on an object that result in a non-zero net force, causing the object to accelerate in the direction of the net force.
Example:
If you kick a soccer ball, the force of your foot creates unbalanced forces on the ball, causing it to accelerate.
Unbalanced Forces
Forces acting on an object that do not cancel each other out, resulting in a non-zero net force and causing the object to accelerate.
Example:
When you kick a soccer ball, the force from your foot is an unbalanced force that causes the ball to accelerate from rest.
Vector Addition
The process of combining forces by considering both their magnitudes and directions to find the resultant net force.
Example:
To find the total force on a boat being pulled by two ropes at different angles, you must use vector addition to combine the tension forces.
Vectors
Physical quantities that have both magnitude and direction, such as force, velocity, and displacement.
Example:
When analyzing forces on a ramp, you must treat them as vectors, considering both their strength and the angle at which they act.