Understanding Forces: Gravity, Friction

• Forces can change the motion of an object.

Gravity and Friction

• Contact forces and non-contact forces are different types of forces.
• The law of universal gravitation explains gravitational forces.
• Friction impacts how two objects move when sliding against each other.

Types of Forces

• A force is any push or pull on an object.
• Forces are measured in newtons (N).

Contact Force

• A push or pull on one object by another that is touching it.
• Examples include pushing a container, pressing on computer keys and dealing with friction.

Noncontact Force

• A push or pull on one object by another without touching it.
• Examples include gravity, magnetic, and electrical forces.

Types of Friction

• Friction resists the motion of two objects that are touching.
• The three types of friction: static, sliding and fluid.

Static Friction

• Prevents objects from moving or 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).

Static Friction vs. Sliding Friction

• With Static Friction, force applied is 100N with static friction of -100N, so net force is 0N.
• With Sliding Friction, force applied is 200N with sliding friction of -70N, so net force is 130N.

Gravity

• Is an attractive force between all objects with mass.
• Mass is the amount of matter in an object.
• The more mass, the more gravitational pull.
• The greater the distance, the less gravitational pull.

Weight vs. Mass

• Weight is the amount of gravitational force exerted on an object, measured in newtons (N).
• An astronaut weighing 539N with a mass of 55kg on Earth would experience a weight change on the moon.
• The astronaut's weight would be less on the moon.

Non-contact Force: Electrical pg. 679

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

Non-contact Force: Magnetic

• A magnet attracts metal iron.
• A magnetic pole is the 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.
• The size of a magnet affects magnetic strength.
• Distance affects magnetic strength.

Explore the effects of forces on object motion, differentiating between contact and non-contact forces. Understand gravity through the law of universal gravitation, and examine the impact of friction on sliding objects, including static and sliding friction.