Vectors, Motion, Newton's Laws, and Stopping Distances

Vocabulary review flashcards covering key definitions, mathematical relationships, laws of motion, and stopping distance factors from the physics lecture notes.

Vector

A physical quantity that has both magnitude and a specific direction, meaning its value can be positive or negative depending on the chosen coordinate frame.

Scalar

A physical quantity that possesses only magnitude and generally cannot be negative (e.g., speed, distance, time, mass, and energy).

Displacement-Time Graph

A graph whose gradient represents velocity, where a horizontal line indicates the object is stationary, a curved line indicates changing velocity (acceleration), and the area underneath equals nothing.

Velocity-Time Graph

A graph whose gradient represents acceleration, where a horizontal line represents constant speed, and the area under the line equals the distance travelled.

Average Speed

The measure used when speed varies over a journey, calculated by dividing the total distance travelled by the total time taken.

Light Gate

An electronic sensor used to measure speed by recording the exact time taken for an object to travel between two points, eliminating human reaction time and stopwatch error.

Acceleration Due to Gravity ($g$)

The uniform rate of acceleration experienced by an object in free fall near Earth, taken as $g = 10\,ms^{-2}$.

Newton’s First Law

The principle stating that an object maintains a constant velocity (or remains at rest) unless acted upon by a non-zero resultant force.

Newton’s Second Law

The law stating that the resultant force on an object is equal to its mass multiplied by its acceleration ($F = ma$), or the rate of change of momentum over time ($F = \frac{mv - mu}{t}$).

Newton’s Third Law

The principle stating that every action force produces an equal and opposite reaction force between interacting bodies.

Centripetal Force

The resultant force directed towards the centre of a circular path that causes an object moving at constant speed to constantly change direction and accelerate.

Inertial Mass

A measure of how difficult it is to change the velocity of an object (including from rest), defined as $\text{inertial mass} = \frac{\text{force}}{\text{acceleration}}$.

Momentum

A vector quantity defined as the product of an object's mass and its velocity ($p = mv$), measured in units of $kg\,ms^{-1}$.

Conservation of Momentum

The principle that the total momentum before a collision equals the total momentum after the collision, provided no external forces act.

Ruler Drop Experiment

A test used to measure human reaction time by dropping a ruler without warning and converting the distance fallen before catching it into a time value.

Human Reaction Time

The delay between observing an event and executing a physical response, which averages around $0.25\,\text{seconds}$ ($250\,\text{milliseconds}$).

Thinking Distance

The distance a vehicle travels during the driver's reaction time, influenced by vehicle speed, tiredness, distractions, concentration, and alcohol or drugs.

Braking Distance

The distance a vehicle travels from the moment the brakes are applied until it stops, affected by vehicle speed, road conditions, tyre tread, brake pad condition, and vehicle mass.

Typical Stopping Distances Chart

A visual breakdown illustrating how thinking distance and braking distance scale with initial vehicle speed to determine total stopping distance.

Large Deceleration Impact

A rapid loss of high velocity over a very short time in a collision that produces an extremely large force ($F = ma$ or $F = \frac{\Delta p}{t}$), posing severe risk of passenger injury.

Work Done to Stop

The mechanical work done by friction to stop a moving vehicle, which equals the vehicle's initial kinetic energy ($\text{Work Done} = KE = Fd = \frac{1}{2}mu^2$), showing that braking distance is proportional to the square of initial velocity.