Forces and Motion: Contact and Non-Contact Forces

• Forces can change the motion of an object.

Contact and Non-Contact Forces

• Contact forces occur when objects are touching.
• Non-contact forces occur when objects are not touching.

Force

• Force is a push or a pull on an object.
• Forces are measured in Newtons (N).

Types of Contact Forces

• Pushing on a container.
• Pressing on computer keys.
• Friction.

Types of Non-Contact Forces

• Gravity.
• Magnetic.
• Electrical.

Friction

• Friction is a force that resists the motion of two objects that are touching.

Static Friction

• Prevents objects from sliding past each other.

Sliding Friction

• Opposes the motion of objects sliding past each other.

Fluid Friction

• Friction between a surface and a fluid such as water or air (air resistance).

Gravity

• An attractive force that exists between objects that have mass.

Mass

• The amount of matter in an object.
• The more mass, the more gravitational pull.
• An object's mass would remain the same on the moon.

Distance

• The greater the distance, the less gravitational pull.

Weight

• The amount of gravitational force exerted on an object.
• Weight is measured in Newtons (N).
• Weight would be less on the moon because mass would remain consistent.

Static Charge

• An unbalanced positive or negative charge on an object.
• Opposite charges attract each other.
• The same charges repel each other.
• The more the amount of charge, the greater the electrical force (attraction or repulsion).
• The more distance, the less electrical force.

Magnet

• An object that attracts metal iron.

Magnetic Pole

• A place on a magnet where the force it applies is the strongest.
• Opposite poles (charges) attract each other.
• The same poles (charges) repel each other.
• Variables that affect magnetic strength are the size of magnet and distance.
• The further away magnets are, the weaker the magnetic force.