Magnets attract certain metal objects, a phenomenon easily observed with a paperclip. This raises the question of why a typical magnet cannot pull a car. The inability stems from the nature of magnetism and the substantial forces resisting a car’s movement.
How Magnets Exert Force
Magnetism originates from the motion of electric charges, generating a magnetic field. This field extends around a magnet, its strength and direction determining the potential for magnetic force. It strongly interacts with ferromagnetic substances like iron, nickel, cobalt, and their alloys such as steel.
These materials contain tiny magnetic moments, due to electron spin. These moments group into microscopic areas called magnetic domains, where the moments within each domain are aligned.
In an unmagnetized ferromagnetic material, these individual magnetic domains are oriented randomly, causing their magnetic effects to largely cancel each other out. When an external magnet’s field is brought near, it encourages these domains to rotate and align with the external field. This alignment transforms the material into a temporary magnet, attracted to the external magnet. The collective alignment creates a strong attractive force.
Why Magnetic Force is Limited
The strength of magnetic force diminishes rapidly with distance. For typical magnets, the magnetic field strength decreases approximately with the cube of the distance. Doubling the distance reduces the field strength to one-eighth of its original value, making the attractive force negligible even a short distance away.
The amount and type of magnetic material in an object also influence the attraction. While a car contains steel, it is a complex assembly of various components, not a solid block of highly magnetic metal. A car’s structure is often thin, shaped, and combined with non-magnetic materials, which dilutes the overall magnetic response. This contrasts with a small, solid iron object like a paperclip, which presents a concentrated target for magnetic attraction.
Different types of magnets also possess varying strengths. Permanent magnets, like those on a refrigerator, have a fixed magnetic field. Electromagnets, which use electric current to generate magnetism, can be considerably stronger than permanent magnets. However, even powerful electromagnets are designed for specialized industrial uses, such as lifting scrap metal, not for moving passenger vehicles.
The Forces Opposing a Car’s Movement
Beyond the limitations of magnetic force, a car presents significant resistance to movement. A typical passenger vehicle weighs around 3,800 to 4,400 pounds (approximately 1,700 to 2,000 kilograms), representing a substantial mass. This mass gives the car significant inertia, meaning it resists any change to its state of motion, whether at rest or in motion. The force of gravity also acts continuously, pressing the vehicle firmly against the ground.
Moving such a heavy object also requires overcoming significant frictional forces. Rolling resistance, generated by the deformation of tires and their interaction with the road surface, constantly opposes motion. Air resistance, or drag, acts against the car’s movement, increasing significantly with speed.
The combined magnitude of these forces—inertia, gravity, rolling resistance, and air resistance—is immense. To put a car into motion, let alone lift it, a magnet would need to generate a force far exceeding the sum of these resistive forces. The maximum attractive force an ordinary magnet can produce is simply dwarfed by the sheer scale of the forces involved in moving a multi-ton vehicle.