Contact Forces and Non-Contact Forces
Contact Forces and Non-Contact Forces
This lesson aligns with NGSS PS2.B
Introduction
In the realm of physics, understanding the forces that govern interactions between objects is crucial. Forces are fundamental to explaining motion, stability, and the behavior of matter in the universe. Two broad categories of forces, namely contact forces and non-contact forces, play significant roles in shaping our physical world. In this comprehensive article, we will delve into the concepts of contact forces and non-contact forces, explore their characteristics, and provide real-life examples to elucidate their effects.
Contact Forces
Contact forces arise when two objects come into direct physical contact with each other. These forces result from the interaction of surfaces and are transmitted through direct touch. Let's explore some common examples of contact forces:
Friction:
Friction is a contact force that opposes the relative motion or tendency of motion between surfaces in contact. It occurs when two objects rub against each other. For instance, the friction between the tires of a car and the road surface enables the car to accelerate, decelerate, or maintain a constant speed.
Normal Force:
The normal force is a contact force exerted by a surface to support the weight of an object resting on it. When you sit on a chair, the chair exerts an upward normal force to counteract the downward force of gravity pulling you towards the Earth.

Tension:
Tension is a contact force transmitted through a string, rope, or cable when it is pulled taut. For example, the tension in a rope holding a swinging pendulum or the tension in a stretched rubber band are instances of contact forces at work.

Applied Force:
Applied force is exerted by a person or object on another object through direct contact. Pushing a box across the floor or lifting a book are examples of applied forces.
Non-Contact Forces
When you jump from the floor, you always return to the surface. This phenomenon can be attributed to gravity, a non-contact force that pulls objects towards the Earth. Similarly, when you throw a ball high up in the air, it reaches its highest point before being pulled back towards the ground by the force of gravity. In both cases, there is no physical contact holding your feet or the ball in place; instead, the gravitational force acts at a distance, causing the objects to move towards the Earth's surface.
Unlike contact forces, non-contact forces act at a distance without any physical contact between the interacting objects. These forces occur through fields that permeate space. Here are some examples of non-contact forces:
Gravity:
Gravity is one of the most familiar non-contact forces, responsible for the attraction between objects with mass. It is the force that keeps planets in orbit around the sun and objects on the Earth's surface grounded. For instance, the gravitational force between the Earth and an apple causes the apple to fall towards the ground.

Electrostatic Force:
Electrostatic force is the force between electrically charged objects. Objects with like charges repel each other, while objects with opposite charges attract. For example, when you rub a balloon against your hair, the balloon becomes negatively charged and can stick to a wall due to the electrostatic force.
Magnetic Force:
Magnetic force is the force exerted between magnets or magnetic materials. Like charges repel each other, while opposite charges attract. For instance, the magnetic force between a magnet and a piece of iron causes the iron to be attracted towards the magnet.
Gravitational Force:
Gravitational force is the force exerted between any two objects with mass. It is an attractive force that acts on all objects in the universe. For example, the gravitational force between the Earth and the Moon keeps the Moon in orbit around the Earth.
Examples of Contact and Non-Contact Forces in Everyday Life
Now, let's explore some everyday examples to illustrate the distinctions between contact and non-contact forces:
Pushing a Shopping Cart:
When you push a shopping cart at the grocery store, you exert a contact force on the cart. The force of your hands against the cart's handle initiates motion, overcoming the friction between the wheels and the floor.

Playing with Magnets:
When you bring two magnets close together, you can feel the magnetic force either attracting or repelling them, depending on their orientations. This interaction demonstrates a non-contact force at work.
Walking:
As you walk, your feet exert a contact force on the ground, propelling you forward. Simultaneously, the ground exerts an equal and opposite contact force (friction) to enable your forward movement.
Balloon Sticking to a Wall:
After rubbing a balloon against your hair, it becomes negatively charged. When you place the balloon near a wall, the electrostatic force between the charged balloon and the neutral wall causes the balloon to stick to the wall.
Conclusion
- Contact forces arise when two objects come into direct physical contact with each other. These forces result from the interaction of surfaces and are transmitted through direct touch.
- Tension is a contact force transmitted through a string, rope, or cable when it is pulled taut.
- When you jump from the floor, you always return to the surface. This phenomenon can be attributed to gravity, a non-contact force that pulls objects towards the Earth.
- Gravity is one of the most familiar non-contact forces, responsible for the attraction between objects with mass.
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