Forces, Gravity and Friction

• Forces can change the motion of an object.

Gravity and Friction

• Contact forces and non-contact forces exist.
• The law of universal gravitation describes gravity.
• Friction impacts how objects move past each other.

Types of Forces

• Force is a push or pull on an object.
• Contact force occurs when objects touch
• Non-contact force involves pushes or pulls without touching, like gravity

Types of Friction

• Friction is a force resisting motion between touching objects.
• Static friction prevents objects from sliding.
• Sliding friction opposes the motion of sliding objects.
• Fluid friction occurs between a surface and a fluid like water or air (air resistance).

Static vs Sliding Friction

• Net force is 0N when there is static friction.
• Sliding friction -70N with applied force of 200N

Impact Mass and Distance on Gravity

• Gravity is an attractive force between all matter.
• Mass is the amount of matter in an object.
• More mass leads to greater gravitational pull.
• Greater distance reduces gravitational pull.

Weight and Mass

• Weight is the amount of gravitational force, F=ma.
• Weight decreases on the moon for an astronaut with a mass of 55kg and 539N on earth.

Electrical Non-Contact Force

• Static charge is unbalanced positive or negative charge.
• Opposite charges attract.
• Like charges repel.
• More charge increases electrical force (attraction or repulsion).
• Greater distance reduces electrical force.

Magnetic Non-Contact Force

• A magnet attracts metal iron.
• A magnetic pole is where the magnet's force is strongest.
• Opposite magnetic poles attract.
• Like magnetic poles repel.
• Larger magnets have greater magnetic strength.
• Magnetic force weakens with greater distance.

Forces alter the motion of objects through contact and non-contact interactions. Gravity, described by the law of universal gravitation, is a key non-contact force. Friction, encompassing static, sliding, and fluid types, opposes motion between objects.