Contact Forces
This force directly opposes the relative sliding motion between two solid surfaces as microscopic ridges interlock.
What is friction (or frictional resistance)?
This noncontact attractive force pulls any two masses toward each other across empty space.
What is gravity (or gravitational force)?
Two magnetic north poles positioned next to one another will exhibit this mutual noncontact reaction.
What is repulsion (or repelling each other)?
This term identifies the invisible region surrounding a mass, magnet, or charge where it exerts a force on susceptible objects.
What is a force field (or field)?
An astronaut running on an International Space Station treadmill relies on this contact force between running shoes and the belt to propel forward.
What is friction?
This perpendicular support force is exerted by a stable surface to counterbalance the weight of an object resting upon it.
What is the normal force?
Unlike magnetic or electric forces that can both push and pull, gravitational force is always limited to this single type of interaction.
What is attractive (or attraction)?
These two distinct varieties of electric charge exert an attractive force on each other across an electric field.
What are positive and negative charges?
As the separation distance between two interacting charged particles increases, their field strength undergoes this change.
What is decreases (or weakens / drops off)?
A handheld navigational compass functions because its needle aligns with this global noncontact field.
What is Earth's magnetic field (or magnetism)?
This mechanical force occurs whenever a person or object directly pushes or pulls another item, such as a foot kicking a soccer ball.
What is an applied force?
This massive body exerts the gravitational field that keeps the Moon locked in steady planetary orbit without any physical contact.
What is Earth?
A plastic comb attracts dry strands of hair from two inches away because of this static phenomenon.
What is electrostatic force (or static electricity)?
Noncontact forces are unique because they can exert pushes and pulls across this matter-free environment.
What is a vacuum (or empty space / outer space)?
A hockey puck glides much further across smooth ice than asphalt because the ice offers exceptionally low levels of this contact force.
What is friction (or frictional resistance)?
Surface friction actively converts kinetic energy into sound and this other primary form of energy.
What is thermal energy (or heat)?
The strength of gravitational attraction between two objects depends on the distance separating them and this fundamental quantity of matter within them.
What is mass?
Permanent magnetic dipoles produce fields that exert significant attraction over objects containing this common ferromagnetic metal.
What is iron?
When two opposing magnetic poles transition from a moderate separation to close proximity, their attractive force experiences this change.
What is increases drastically (or peaks / strengthens)?
Applied force, tension, and normal force all belong to this broad classification requiring direct matter-to-matter touch.
What are contact forces?
Colliding atmospheric gas molecules exert this specific resistive contact force upward against a skydiver's open nylon parachute.
What is air resistance (or drag)?
State whether this claim is true or false: Gravitational fields require atmospheric air molecules to transmit force across spatial gaps.
What is false? (Gravity acts across a vacuum without needing air.)
This electrostatic process occurs when excess surface electrons on an insulator pull neutral atoms toward it without direct touching.
What is charge induction (or electrostatic induction)?
This specific noncontact field is responsible for keeping Earth's oceans and atmosphere anchored to its surface.
What is Earth's gravitational field (or gravity)?
A heavy crate sliding to a stop on concrete and a parachute braking a space capsule are both examples of interactions dominated by this force classification.
What are contact forces?