Mechanics and materials flashcards

Mechanics and materials covers the fundamental principles governing how objects move and how materials respond to forces. Students must understand scalar and vector quantities, and be able to resolve forces and velocities into components. Key areas include Newton's three laws of motion, momentum and impulse, and the equations of uniform acceleration. Energy concepts such as kinetic energy, gravitational potential energy, and the work-energy theorem are essential. Projectile motion requires treating horizontal and vertical components independently. For materials, students need to understand stress, strain, and the Young modulus, as well as interpreting force-extension graphs, including Hooke's law, the elastic limit, and plastic deformation. Understanding the difference between elastic and plastic behaviour, and being able to calculate energy stored in a stretched material, are also required. These ideas underpin much of the rest of A-Level Physics.

1. Card 1

   What is the difference between a scalar and a vector quantity?

   A scalar has magnitude only, while a vector has both magnitude and direction. Speed is scalar; velocity is vector.

2. Card 2

   State Newton's second law of motion in terms of momentum.

   The net force on an object equals the rate of change of momentum: F = change in momentum / time, or F = ma when mass is constant.

3. Card 3

   What is the principle of conservation of momentum?

   In a closed system with no external forces, the total momentum before a collision equals the total momentum after. It is always conserved.

4. Card 4

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

   The area under a force-time graph equals impulse, which is the change in momentum of the object. Impulse = F x delta t.

5. Card 5

   State Hooke's law and the condition under which it applies.

   Force is proportional to extension: F = k x e, where k is the spring constant. This holds only up to the limit of proportionality.

6. Card 6

   How is the Young modulus defined?

   Young modulus E = stress / strain = (F/A) / (x/L). It measures a material's stiffness and has units of pascals (Pa).

7. Card 7

   What is the difference between elastic and plastic deformation?

   Elastic deformation is fully reversible when the force is removed. Plastic deformation is permanent; the material does not return to its original shape.

8. Card 8

   How do you calculate the energy stored in a stretched spring obeying Hooke's law?

   Energy stored = 1/2 x k x e^2, or equivalently 1/2 x F x e. This equals the elastic potential energy and is the area under the force-extension graph.

9. Card 9

   What assumptions are made in projectile motion calculations?

   Air resistance is ignored, and gravitational acceleration g acts only vertically. Horizontal velocity remains constant throughout the motion.

10. Card 10

    Define stress and strain for a material under tension.

    Stress = force / cross-sectional area (Pa). Strain = extension / original length (dimensionless). Both describe how a material responds to an applied load.

11. Card 11

    What is the work-energy theorem?

    The net work done on an object equals its change in kinetic energy. W = delta(KE) = 1/2 mv^2 - 1/2 mu^2.

12. Card 12

    What distinguishes a brittle material from a ductile material on a stress-strain graph?

    A brittle material fractures with little or no plastic deformation. A ductile material shows a large plastic region before fracture, like copper.

• Many students confuse mass and weight, forgetting that weight is a force equal to mass multiplied by gravitational field strength and is measured in newtons, not kilograms.
• When analysing projectile motion, students often incorrectly apply the equations of uniform acceleration to the horizontal direction, not realising that horizontal velocity is constant and only the vertical component accelerates.
• Students frequently use the formula E = 1/2 F x e for energy stored in a spring even beyond the elastic limit, when in fact this only applies while the material obeys Hooke's law and the force-extension graph remains linear.

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