Physics Forces Vocabulary

A set of vocabulary flashcards defining key physics concepts related to forces, motion, and Newton's laws based on the lecture notes.

Weight

The force of gravity of the planet, star, or moon acting on an object, acting vertically downwards according to the formula $w = mg$.

Contact force / Normal Reaction Force

A force acting between two bodies that are in contact with each other, directed $90^\bullet$ away from the surface of the object that is exerting the force.

Friction

The force between bodies that are sliding past one another or tend to slide past one another, which acts opposite to motion and parallel to the surface, converting energy into heat during motion.

Drag / Air Resistance

A type of frictional force exerted by fluids (gas and liquid) on bodies moving through them, opposing motion and increasing with speed, surface area, and density of fluid.

Upthrust

A force exerted upwards by fluids (gas and liquid) on objects immersed in them, which acts whether there is motion or no motion.

Tension

A force exerted by ropes, strings, rods, etc., that are being stretched, which always pulls on the object attached to them.

Free body diagrams

Diagrams that show all the forces acting on a single body, while omitting all other objects.

Newton's 1st law

States that a body will continue in its state of rest or motion unless a resultant force acts on it.

Newton's 2nd law

States that the acceleration of a body of constant mass is directly proportional to the resultant force, and in the same direction as the resultant force.

Newton's 3rd Law

States that if body A exerts a force on body B, then body B will exert an equal and opposite force on body A.

Action-Reaction pair

A pair of forces under Newton's 3rd law that are equal and opposite, of the same type of force, and exerted on each other by two objects.

Thinking distance

The distance covered during a driver's reaction time, which depends on the skill/attentiveness of the driver, visibility, and initial speed.

Braking Distance

The distance covered from when the brakes are applied to when the car comes to rest, which depends on road conditions, tyre conditions, braking force, initial speed, and mass of the car.

Stopping distance

The total distance covered during stopping, defined by the formula $\text{Stopping distance} = \text{Thinking distance} + \text{Braking distance}$.