Glossary
Action-Reaction Pairs
Two forces that are equal in magnitude and opposite in direction, acting on different objects, as described by Newton's Third Law.
Example:
When you jump, your feet push down on the Earth (action), and the Earth pushes up on your feet (reaction), forming an action-reaction pair that propels you upward.
Applied Force
A force exerted on an object by a person or another object through direct physical contact.
Example:
Pushing a swing to make it move involves an applied force from your hand.
Contact Forces
Forces that occur when two objects are physically touching each other.
Example:
The push you give a door to open it, or the friction between tires and the road, are examples of contact forces.
Direction
The orientation or path along which a vector quantity acts, indicating its spatial alignment.
Example:
When a compass points north, it indicates a specific direction for navigation.
Equilibrium
A state where the net force acting on an object is zero, resulting in either constant velocity or zero acceleration.
Example:
A book resting motionless on a table is in equilibrium because the normal force perfectly balances the force of gravity.
Field Forces
Forces that act on an object without direct physical contact, through a force field.
Example:
The Earth's gravity pulling on a satellite in orbit is a field force, acting across empty space.
Force
A push or a pull that can cause an object to accelerate, change its velocity, or deform.
Example:
Applying a force to a shopping cart makes it move across the aisle.
Force Interaction
The mutual influence between two or more objects that results in forces being exerted on each other.
Example:
When a bat hits a baseball, there is a force interaction between them, causing both to change motion.
Force of Friction
A force that opposes relative motion or attempted motion between two surfaces in contact.
Example:
The force of friction between your shoes and the ground allows you to walk without slipping, providing necessary grip.
Free-Body Diagram (FBD)
A visual representation showing all external forces acting on a single object, typically drawn as a dot or box.
Example:
Drawing an FBD for a book resting on a table helps identify the normal force and gravity acting on it.
Magnitude
The numerical size or amount of a physical quantity, often representing the strength or extent of a vector.
Example:
The magnitude of a car's velocity might be 60 mph, regardless of its direction.
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).
Example:
A lighter car will have a greater acceleration than a heavier car when the same Newton's Second Law force is applied by the engine.
Newton's Third Law
States that for every action, there is an equal and opposite reaction.
Example:
When a rocket expels gas downward, the gas exerts an equal and opposite upward force on the rocket, demonstrating Newton's Third Law and propelling it into space.
Normal Force
The perpendicular contact force exerted by a surface on an object resting on it, preventing the object from passing through the surface.
Example:
When you stand on the floor, the floor exerts an upward normal force on your feet, supporting your body.
Resultant Force (Net Force)
The single force that represents the vector sum of all individual forces acting on an object.
Example:
If two people push a box in the same direction, the resultant force is the sum of their individual pushes, making the box accelerate faster.
Spring Force
The restorative force exerted by a spring, which is proportional to its displacement from its equilibrium position (Hooke's Law).
Example:
When you compress a toy dart gun, the spring force builds up, ready to launch the dart when released.
Tension
The pulling force transmitted axially by means of a string, cable, chain, or similar one-dimensional continuous object.
Example:
The tension in a rope supports a rock climber hanging from it, preventing them from falling.
Vector
A physical quantity that has both magnitude (size) and direction.
Example:
A soccer player kicks the ball with a vector of 20 m/s towards the goal.
Weight (Force of Gravity)
The gravitational force exerted by a planet on an object, always directed downwards towards the center of the planet.
Example:
An astronaut's weight on the Moon is significantly less than on Earth due to the Moon's weaker gravitational pull.