PhysicsInvisible Pushes and Pulls: Gravity, Magnets, and Electric Fields
Lumi floats in a softly glowing lab, holding two bar magnets that hover apart, a dropped ball arcing toward the floor, and a balloon lifting paper bits, faint field lines drawn in the air between everything.
- Identify three forces that act between objects without those objects touching.
- Explain that a field is the region around an object where it can push or pull another object.
- Predict how a non-contact force changes when the distance between objects increases or decreases.
- Relate the strength of gravity, magnetism, and electric force to a property of the objects (mass or charge).
Key terms
- Non-contact force
- A push or pull that acts between objects that are not touching each other.
- Field
- The invisible region around an object where it can push or pull other objects.
- Gravity
- The attractive force between objects that depends on their mass and separation.
- Electric force
- The push or pull between charged objects, stronger when the charge is greater.
Reaching Across Empty Space
Contact forces, like a hand on a cart, need objects to touch, but gravity, magnetism, and the electric force act across a gap with nothing in between. Scientists explain this with the idea of a field, an invisible region surrounding an object that can push or pull anything inside it. The field is strongest close to the object and fades with distance, much like the glow of a lamp lights a room without ever touching you.
What Sets the Strength
Two things decide how strong a non-contact force is. The first is distance: bringing objects closer strengthens the force, while moving them apart weakens it. The second is a property of the objects themselves — mass for gravity, and charge or magnetism for the electric and magnetic forces. This is why Earth's huge mass pulls hard on a falling ball while a pencil's tiny mass produces a pull far too weak to ever notice.
Worked examples
Decide whether a falling apple involves a contact or non-contact force.
- Check whether anything is touching the apple as it falls.
- Nothing touches it, yet Earth's gravity still pulls it down.
- Gravity acts through a field across empty space.
Answer: It is a non-contact force (gravity).
Predict the force change as two magnets are pulled farther apart.
- Recall that non-contact forces weaken with distance.
- Increasing the separation reduces the strength of the magnetic field between them.
- So the pulling force between the magnets gets smaller.
Answer: The force gets weaker.
Activity
Sort each example into contact force or non-contact (field) force.
Practice
Sort six everyday examples into contact forces and non-contact field forces.
Predict how the pull between two magnets changes as you slide them closer together.
Common mistakes to avoid
- Objects must be touching to exert a force.Gravity, magnetism, and electric force act through fields across empty space with no contact needed.
- Air pressure is what makes objects fall.Objects fall because of gravity, which still acts in a vacuum where there is no air at all.
Check your understanding
A ball falls to the ground after you let go of it. Why does it move even though nothing is touching it?
You slowly move two magnets farther apart. What happens to the force between them?
Which statement about non-contact forces is TRUE?
Earth's gravitational field is strong enough to hold the Moon in orbit, but a pencil's gravitational field is far too weak to notice. What property of the objects explains this difference?
Recap
Gravity, magnetism, and the electric force act across empty space through invisible fields, growing stronger when objects are closer and when their mass, charge, or magnetism is greater.
Reflect
Where in your daily life do you notice forces acting on things without anything actually touching them?