Explain · Serious version
Newton's laws of motion in terms of a supermarket trolley
Newton's laws of motion describe the fundamental relationship between the movement of an object and the forces acting upon it.
The first law, inertia, is clearly observed in an empty trolley in the Tesco car park. Left alone, it remains stationary against the kerb until acted upon by a bored teenager or a gale force wind. Once it is trundling towards a parked hatchback, it will continue in its straight line of pathologised misery indefinitely, refusing to stop until it strikes an immovable object or you intervene with your own shins.
The second law explains the relationship between force, mass and acceleration through your trolley's variable load. Pushing an empty unit requires little effort, but filling it with crates of lager and frozen lasagnes creates a significant increase in mass. To achieve the same rate of acceleration as you had when the trolley was light, you must apply a considerably greater amount of force. If you attempt to steer while burdened, the trolley will demonstrate its frustration by swerving violently into the floral display.
The third law dictates that for every action, there is an equal and opposite reaction, most frequently felt when your trolley hits a solid pillar. As you deliver the impact, the metal frame transmits the force directly back into your own hands. You effectively push the trolley, and the trolley, with equal coldness, pushes back against your grip. It is a perfect, symmetrical exchange of kinetic energy that serves as a physical reminder of your own lack of spatial awareness.
Where the analogy breaks downA supermarket trolley is hindered by the friction of a wonky castor wheel, whereas Newton's laws assume an idealised environment free from such mechanical incompetence.