Topic 2 Forces and motion

These flashcards cover the fundamental ideas from Pages 2–6 of the lecture: vector vs. scalar quantities, interpretation of motion graphs, speed measurement methods, typical speeds, Newton’s laws, circular motion, momentum, human reaction time, vehicle stopping distances, kinetic energy in braking, and essential equations and problem‐solving skills.

What distinguishes a vector quantity from a scalar quantity?

A vector has both magnitude and direction, whereas a scalar has magnitude only.

Give two examples of vector quantities discussed in the lecture.

Velocity, displacement, acceleration, force or momentum (any two).

Give two examples of scalar quantities discussed in the lecture.

Speed, distance, time, mass or energy (any two).

When can a displacement value be negative?

When the chosen reference point (zero) is above the object so the object lies in the negative direction relative to that reference.

What information does the gradient of a displacement–time graph provide?

The gradient equals the object's velocity.

On a displacement–time graph, what does a horizontal line represent?

The object is stationary (zero velocity).

What does the area under a displacement–time graph represent?

Nothing – area has no physical meaning for a displacement–time graph.

What information does the gradient of a velocity–time graph provide?

The gradient equals the object's acceleration.

On a velocity–time graph, what does the area under the line represent?

The distance (or displacement if vector‐aware) travelled.

State the formula for average speed when speed varies during motion.

Average speed = total distance travelled ÷ total time taken.

Which experimental tool removes human reaction‐time error when measuring speed?

Light gates (timing gates).

Write the equation for speed in symbols.

speed (v) = distance (s) ÷ time (t).

State two typical everyday speeds given in the lecture.

e.g., walking ≈ 1.4 m s⁻¹; wind ≈ 5–7 m s⁻¹; running ≈ 3 m s⁻¹; sound ≈ 340 m s⁻¹, etc.

What constant acceleration does gravity produce near Earth’s surface (per the notes)?

g = 10 m s⁻².

State Newton’s First Law of Motion in simple terms.

An object remains at rest or moves with constant velocity unless acted on by a resultant force.

According to Newton’s First Law, what happens if the resultant force on an object is zero?

The object has no acceleration—either it stays at rest or continues at constant velocity.

Write Newton’s Second Law as an equation.

F = m a (force equals mass times acceleration).

Differentiate between mass and weight.

Mass is the amount of matter (scalar, kg); weight is the gravitational force on that mass (vector, N).

What is the direction of the centripetal force on an object in uniform circular motion?

Toward the centre of the circle.

Why is an object in uniform circular motion considered to be accelerating?

Its velocity is continuously changing direction, so acceleration is present even if speed is constant.

Define inertial mass using a formula.

Inertial mass = force ÷ acceleration (m = F ⁄ a).

State Newton’s Third Law of Motion.

For every action force, there is an equal and opposite reaction force.

Provide an everyday example illustrating Newton’s Third Law.

A rocket: exhaust gases push downward, creating an equal and opposite upward force on the rocket.

Write the formula for linear momentum.

p = m v (momentum equals mass times velocity).

What is always conserved in an isolated collision?

Total momentum before the collision equals total momentum after.

Express Newton’s Second Law in terms of momentum change.

Force = change in momentum ÷ time, F = (m v – m u) ⁄ t.

What is the average human reaction time cited in the lecture?

Approximately 0.25 s (250 ms).

In stopping‐distance terminology, what is ‘thinking distance’?

The distance travelled during the driver’s reaction time before braking begins.

List two factors that increase thinking distance.

Higher speed, fatigue, distractions, alcohol/drugs, poor concentration (any two).

What is ‘braking distance’?

The distance the vehicle travels from the moment brakes are applied until it stops.

List two factors that increase braking distance.

Higher speed, wet/icy roads, worn brake pads, bald tyres, greater vehicle mass (any two).

Why are large decelerations dangerous during a crash?

They create very large forces on occupants (F = m a) which can cause injury.

How does kinetic energy relate to work done in stopping a vehicle?

Work done by brakes equals the vehicle’s initial kinetic energy: W = ½ m u².

How does braking distance vary with initial speed (u)?

Braking distance is proportional to u².

State the basic unit‐conversion skill emphasised under ‘Mathematical skills’.

Converting between, e.g., km h⁻¹ ↔ m s⁻¹, miles h⁻¹ ↔ m s⁻¹, etc.

What calculation do you perform on a velocity–time graph to find total distance?

Compute the area under the curve between the time limits.

Give the average mass of a typical car used for force estimates in the notes.

Approximately 1500 kg.