Edexcel IAL Physics Unit 1 – Mechanics & Materials (Exam Notes)

1.3 Mechanics

1. Uniformly Accelerated Motion (SUVAT)

These equations apply only when acceleration is constant and motion is in one dimension.

s = (u + v)t / 2
v = u + at
s = ut + ½at²
v² = u² + 2as

Symbols:
u = initial velocity (m s⁻¹)
v = final velocity (m s⁻¹)
a = acceleration (m s⁻²)
t = time (s)
s = displacement (m)

2. Graphs of Motion

Displacement–Time Graph

Gradient = velocity
Straight line → constant velocity

Velocity–Time Graph

Gradient = acceleration
Area under graph = displacement

Acceleration–Time Graph

Area under graph = change in velocity

3. Scalars and Vectors

Scalar: magnitude only (speed, mass, energy)
Vector: magnitude and direction (velocity, force, acceleration)

4. Resolving Vectors

A vector can be split into perpendicular components:

Horizontal component = F cos θ
Vertical component = F sin θ

5. Resultant of Two Vectors

At right angles: Pythagoras theorem
At any angle: vector triangle or parallelogram method

6. Projectile Motion

Horizontal motion: constant velocity
Vertical motion: constant acceleration due to gravity (g)
Horizontal and vertical motions are independent

7. Forces and Free-Body Diagrams

Show all forces acting on a body
For extended objects, forces act at the centre of gravity

8. Newton’s Laws of Motion

First Law: Object remains at rest or constant velocity if resultant force is zero.
Second Law:

ΣF = ma

Third Law: Forces between two bodies are equal in magnitude and opposite in direction.

Terminal Velocity: Occurs when resistive forces equal weight, so acceleration becomes zero.

9. Gravitational Field Strength and Weight

g = F / m
Weight: W = mg

10. Momentum

p = mv
Unit: kg m s⁻¹

Conservation of Momentum

Total momentum before collision = total momentum after collision (if no external forces).

11. Moments

Moment of a force = F × perpendicular distance
For equilibrium: clockwise moments = anticlockwise moments

12. Work, Energy and Power

Work Done

ΔW = Fs (component of force in direction of motion)

Kinetic Energy

E_k = ½mv²

Gravitational Potential Energy

ΔE_g = mgΔh

Conservation of Energy

Total energy remains constant in a closed system.

Power

P = E / t
P = W / t

Efficiency

Efficiency = useful energy output / total energy input
Efficiency = useful power output / total power input

1.4 Materials

1. Density

ρ = m / V

2. Upthrust

Upthrust = weight of fluid displaced

3. Viscosity and Stokes’ Law

F = 6πrηv

Valid for small spheres
Laminar flow only
Viscosity depends on temperature

4. Hooke’s Law

ΔF = kΔx

k = stiffness constant

5. Stress and Strain

Stress = Force / Cross-sectional area
Strain = Extension / Original length
Young modulus = Stress / Strain

6. Force–Extension and Stress–Strain Graphs

Limit of proportionality
Elastic limit
Yield point
Plastic deformation
Breaking stress

7. Elastic Strain Energy

ΔE_el = ½FΔx

Equal to the area under the force–extension graph.

Exam Tip: Always state assumptions (constant acceleration, no energy loss, laminar flow) to gain method marks.

Edexcel IAL Physics Unit 1 – Common Exam Questions (Quick Answers)

Explain the difference between scalar and vector quantities.

Scalar quantities have magnitude only (e.g. speed, mass, energy). Vector quantities have both magnitude and direction (e.g. velocity, force, acceleration).

State the conditions under which SUVAT equations can be used.

SUVAT equations apply only when:

Acceleration is constant
Motion is in one dimension

What information can be obtained from motion graphs?

Displacement–time: gradient gives velocity
Velocity–time: gradient gives acceleration, area gives displacement
Acceleration–time: area gives change in velocity

Explain why horizontal and vertical motions are independent in projectile motion.

The only force acting is gravity, which acts vertically downward. There is no horizontal force, so horizontal velocity remains constant while vertical motion is accelerated.

Define terminal velocity.

Terminal velocity is the constant maximum velocity reached when the resistive forces equal the weight, resulting in zero acceleration.

State and explain Newton’s First Law of Motion.

An object remains at rest or moves with constant velocity unless acted upon by a resultant external force. This occurs because zero resultant force means zero acceleration.

State Newton’s Third Law of Motion.

When two bodies interact, they exert forces on each other that are equal in magnitude and opposite in direction, acting on different bodies.

Define momentum and state its unit.

Momentum is defined as p = mv. The SI unit of momentum is kg m s⁻¹.

State the principle of conservation of linear momentum.

The total momentum of a system remains constant provided no external forces act on the system.

Define the moment of a force.

The moment of a force is the product of the force and the perpendicular distance from the line of action of the force to the pivot.

State the condition for equilibrium of a rigid body.

Resultant force is zero
Sum of clockwise moments equals sum of anticlockwise moments

Define work done by a force.

Work done is the product of the force and the displacement in the direction of the force.

State the equations for kinetic and gravitational potential energy.

Kinetic energy: E_k = ½mv²
Gravitational potential energy: ΔE_g = mgΔh

State the principle of conservation of energy.

Energy cannot be created or destroyed; it can only be transferred or transformed from one form to another.

Define power and state its unit.

Power is the rate of energy transfer or work done. Unit: watt (W).

Define efficiency.

Efficiency = useful energy output / total energy input (or useful power output / total power input)

Define density and state its equation.

Density is mass per unit volume. ρ = m / V

State the principle of upthrust.

The upthrust acting on an object is equal to the weight of the fluid displaced by the object.

State Stokes’ Law and its conditions.

F = 6πrηv Applies to small spherical objects moving at low speeds in laminar flow.

State Hooke’s Law.

The extension of a material is directly proportional to the applied force, provided the limit of proportionality is not exceeded.

Define stress, strain and Young modulus.

Stress = Force / cross-sectional area
Strain = Extension / original length
Young modulus = Stress / Strain

What does the area under a force–extension graph represent?

The elastic strain energy stored in the material.

Exam Tip: These questions often appear as 2–4 mark definitions or explanations. Precision of wording is essential.

Edexcel IAL Physics Unit 1 – Predicted Exam Questions (With Answers)

Q1. A particle moves with uniform acceleration. Derive the equation v² = u² + 2as.

From v = u + at, rearrange to t = (v − u)/a.
Substitute into s = (u + v)t / 2:
s = (u + v)(v − u) / (2a)
2as = v² − u²
v² = u² + 2as

Q2. Explain how displacement can be determined from a velocity–time graph.

Displacement is equal to the area under the velocity–time graph. This may be calculated using geometrical shapes or integration.

Q3. A projectile is fired horizontally from a cliff. Explain why its time of flight depends only on vertical motion.

The only force acting is gravity, which acts vertically downward. Horizontal motion has no acceleration, so vertical motion alone determines the time of flight.

Q4. Describe how terminal velocity is reached for a falling object.

As speed increases, resistive force increases. Eventually resistive force equals weight, resulting in zero resultant force and zero acceleration. The object then falls at constant terminal velocity.

Q5. Explain the significance of ΣF = 0 for a moving object.

Zero resultant force implies zero acceleration. The object therefore moves with constant velocity according to Newton’s First Law.

Q6. Two bodies collide and stick together. State and apply the principle used to solve such problems.

The principle of conservation of linear momentum is used. Total momentum before collision equals total momentum after collision, provided no external forces act.

Q7. Explain what is meant by the moment of a force and state its unit.

The moment of a force is the turning effect about a pivot, equal to force multiplied by perpendicular distance. Unit: newton metre (N m).

Q8. A rigid body is in equilibrium. State the two equilibrium conditions.

Resultant force equals zero
Sum of clockwise moments equals sum of anticlockwise moments

Q9. Explain how energy conservation is applied to a falling object.

Loss in gravitational potential energy equals gain in kinetic energy, assuming no energy losses to air resistance.

Q10. A motor lifts a load at constant speed. Explain why power is still required.

Although acceleration is zero, work is done against gravity. Power is required to transfer energy at a constant rate.

Q11. Define density and describe an experimental method to determine it.

Density is mass per unit volume. Measure mass using a balance and volume using displacement or dimensions, then calculate ρ = m / V.

Q12. Explain the origin of upthrust acting on an object in a fluid.

Pressure in a fluid increases with depth. The greater pressure at the bottom produces a net upward force equal to the weight of fluid displaced.

Q13. State Stokes’ Law and explain when it is valid.

Stokes’ Law: F = 6πrηv. Valid for small spherical objects moving slowly in laminar flow.

Q14. Describe how the viscosity of a liquid can be determined using a falling ball.

Measure terminal velocity of the ball. Apply Stokes’ Law and equilibrium of forces to calculate viscosity.

Q15. State Hooke’s Law and explain the limit of proportionality.

Extension is proportional to force provided the limit of proportionality is not exceeded. Beyond this point, extension is no longer proportional to force.

Q16. Explain the difference between elastic and plastic deformation.

Elastic deformation is reversible when the force is removed. Plastic deformation is permanent.

Q17. Define Young modulus and explain what a high value indicates.

Young modulus is the ratio of stress to strain. A high value indicates a stiff material.

Q18. What does the area under a force–extension graph represent?