Contact and Non-Contact Forces

• Define force and differentiate between contact and non-contact forces.

• Identify and describe various types of contact forces, including friction, muscular force, and normal force.

• Identify and describe various types of non-contact forces, including gravitational, magnetic, and electrostatic forces.

• Explain the factors that influence the strength of forces like gravity and friction.

Key Vocabulary

Force

A force is a push or a pull on an object, which is measured in Newtons.

Contact Force

This is a type of force that acts only when two objects are physically touching each other.

Non-Contact Force

This force can act between two objects that are not in direct physical contact with each other.

Friction

Friction is a contact force that opposes the motion between two surfaces touching each other.

Gravity

Gravity is a non-contact force that pulls objects toward each other depending on their mass.

Contact Forces

• ​These are forces that act on an object through direct physical touch.

• ​​For the force to have an effect, the objects must be touching.

• ​Kicking a soccer ball is an example of a contact force.

Non-Contact Forces

• ​These forces can push or pull an object without physically touching it.

• ​​They can act from a distance, so the objects do not need to touch.

• ​A magnet pulling paper clips is an example of a non-contact force.

Types of Contact Forces

• Muscular force is made by your body for movement and even breathing.

• An applied force is a direct push or pull, like pushing a cart.

• Normal force is the support a surface gives to an object on it.

• Tension pulls through a rope; spring force restores a spring’s original shape.

The Force of Friction

• Friction is a contact force that opposes the motion between two surfaces.

• It is caused by irregularities on surfaces, even ones that seem smooth.

• Air resistance is friction that pushes on objects moving through the air.

• Friction can be helpful by providing grip or cause wear on machine parts.

Non-Contact Forces

Gravitational Force

• ​This force pulls all objects with mass toward one another.

• ​​Its strength depends on the mass of the objects and their distance.

• ​An object's weight is the measure of gravity's force on it.

Magnetic Force

• ​This force acts between magnets and certain metals like iron.

• ​​Every magnet has a north pole and a south pole.

• ​Opposite poles attract, while like poles will repel each other.

Electrostatic Force

• ​This is the push or pull between electrically charged objects.

• ​​Objects can have a positive or a negative electric charge.

• ​Like charges repel, while opposite charges will attract one another.

• A force is a push or a pull, measured in Newtons.

• Forces are either contact (requiring touch) or non-contact (acting at a distance).

• Contact forces include friction, tension, and muscular force.

• Non-contact forces include gravity, magnetic, and electrostatic forces.

• Gravity depends on mass and distance, while friction depends on surface texture.

• Understanding forces helps explain why objects move or stay still.