Physics: Motion

What is distance?

The total length of the path travelled by an object.

What is displacement?

The straight-line distance from the starting point to the ending point in a specified direction.

Is distance a scalar or vector quantity?

Scalar.

Is displacement a scalar or vector quantity?

Vector.

What is average speed?

Total distance travelled divided by total time taken.

What is the equation for average speed?

Average speed = Total distance ÷ Total time.

What is average velocity?

Total displacement divided by total time taken.

What is the equation for average velocity?

Average velocity = Total displacement ÷ Total time.

What happens to displacement when an object returns to its starting point?

The displacement is zero.

What is instantaneous velocity?

The velocity of an object at a specific moment in time.

How is instantaneous velocity found on a displacement-time graph?

By finding the gradient of the tangent at that point.

What is speed?

The rate of change of distance.

What is velocity?

The rate of change of displacement.

What is the equation for velocity?

v = Δs ÷ Δt.

What does the gradient of a displacement-time graph represent?

Velocity.

What does the gradient of a distance-time graph represent?

Speed.

What is acceleration?

The rate of change of velocity.

What is the equation for acceleration?

a = Δv ÷ Δt.

What are the units of acceleration?

m s⁻².

What does the gradient of a velocity-time graph represent?

Acceleration.

How is instantaneous acceleration found on a velocity-time graph?

By finding the gradient of the tangent.

What does the area under a velocity-time graph represent?

Displacement.

When can the SUVAT equations be used?

When acceleration is constant.

What does u represent in SUVAT equations?

Initial velocity.

What does v represent in SUVAT equations?

Final velocity.

What does a represent in SUVAT equations?

Acceleration.

What does s represent in SUVAT equations?

Displacement.

What does t represent in SUVAT equations?

Time.

State the first SUVAT equation.

v = u + at.

State the second SUVAT equation.

v² = u² + 2as.

State the third SUVAT equation.

s = ut + ½at².

State the fourth SUVAT equation.

s = (u + v)t ÷ 2.

What should you write down first when solving a motion problem?

SUVAT.

What is meant by “from rest”?

Initial velocity equals zero.

When is acceleration positive?

When it acts in the same direction as the velocity.

When is acceleration negative?

When it acts opposite to the velocity.

What is the acceleration of a freely falling object near Earth?

9.81 m s⁻² downward.

What symbol is used for gravitational acceleration?

g.

What is the value of g near Earth’s surface?

9.81 m s⁻².

Why is acceleration negative for an object thrown upwards?

Because acceleration acts downward while velocity acts upward.

What is the velocity of an object at its maximum height?

Zero.

Which SUVAT equation is commonly used to find maximum height?

v² = u² + 2as.

What experiment can be used to measure g?

Dropping a ball from different heights and measuring the time taken.

What quantities are measured in the free-fall experiment?

Height and time.

What graph is plotted to determine g in the free-fall experiment?

Height against time squared.

Why is a graph of h against t² used?

Because h = ½gt².

What is the gradient of a graph of h against t²?

½g.

How is g calculated from the gradient?

g = 2 × gradient.

Why does increasing the drop height reduce percentage uncertainty?

Because the measured time becomes larger.

What device can eliminate human reaction time errors in measuring g?

An electromagnet and trapdoor system.

What is the purpose of the trapdoor in the g experiment?

To automatically stop the timer when the ball lands.

What equipment can measure instantaneous velocity?

Light gates.

How can light gates be used to calculate acceleration?

By measuring initial and final velocities and using SUVAT equations.

What is the equation of a straight line?

y = mx + c.

Which SUVAT equation can be derived from the gradient of a velocity-time graph?

v = u + at.

Which SUVAT equation can be derived from the area under a velocity-time graph?

s = (u + v)t ÷ 2.

What shape is used to derive s = (u + v)t ÷ 2?

A trapezium.

What is stopping distance?

The total distance travelled before a vehicle comes to a stop.

What is the equation for stopping distance?

Stopping distance = Thinking distance + Braking distance.

What is thinking distance?

The distance travelled during the driver’s reaction time.

What is the equation for thinking distance?

Thinking distance = Speed × Thinking time.

What is braking distance?

The distance travelled while the brakes slow the vehicle to rest.

What equation can be used to derive braking distance?

v² = u² + 2as.

What is the braking distance formula?

Braking distance = −u² ÷ 2a.

Why is braking distance always positive?

Because the acceleration is negative during braking.

What factors increase thinking distance?

Tiredness, alcohol, drugs, distractions, and slower reaction times.

What factors increase braking distance?

Poor tyre conditions, wet roads, icy roads, and greater vehicle mass.

Why does greater vehicle mass increase braking distance?

Because the same braking force produces a smaller deceleration.

What is the equation for kinetic energy?

KE = ½mv².

What happens to kinetic energy if speed doubles?

It quadruples.

What happens to braking distance if speed doubles?

It becomes four times larger.

Why does braking distance increase rapidly with speed?

Because it is proportional to the square of the speed.

Why are high-speed collisions more dangerous?

Because kinetic energy increases with the square of speed.

What does a steeper displacement-time graph indicate?

Greater velocity.

What does a steeper velocity-time graph indicate?

Greater acceleration.

What does a horizontal displacement-time graph indicate?

Zero velocity.

What does a horizontal velocity-time graph indicate?

Zero acceleration.

What does a negative gradient on a velocity-time graph indicate?

Negative acceleration (deceleration).

What does a curved displacement-time graph indicate?

Changing velocity.

What does a curved velocity-time graph indicate?

Changing acceleration.

What is the SI unit of displacement?

Metres (m).

What is the SI unit of velocity?

Metres per second (m s⁻¹).

What is the SI unit of acceleration?

Metres per second squared (m s⁻²).

What is the SI unit of time?

Seconds (s).

What is the SI unit of distance?

Metres (m).

Why is velocity a vector quantity?

Because it has both magnitude and direction.

Why is speed a scalar quantity?

Because it only has magnitude.

Why is displacement a vector quantity?

Because it includes direction.

Why is distance a scalar quantity?

Because it has no direction.

What must be constant for the SUVAT equations to be valid?

Acceleration.

Which graph uses area to calculate displacement?

Velocity-time graph.

Which graph uses gradient to calculate velocity?

Displacement-time graph.

Which graph uses gradient to calculate acceleration?

Velocity-time graph.

How do you calculate a gradient?

Change in y ÷ Change in x.

Why are tangents used on curved graphs?

To find instantaneous rates of change.

What is meant by deceleration?

Negative acceleration that reduces speed.

What happens to velocity as an object reaches maximum height?

It decreases to zero.

What force causes the acceleration g?

Gravity.

Why does a falling object accelerate?

Because gravity acts on it.

What is the most important condition for solving motion problems with SUVAT?

Constant acceleration.