Understanding Force and Gravity

• Force is a push or pull on an object resulting from interaction with another object.
• Forces are measured using a dynamometer, with the unit of measure being the newton (N).
• 1 N is the force needed to accelerate a 1 kg object at 1 m/s².
• Forces are classified into contact forces and action-at-a-distance forces.
• Contact forces occur when the body exerting the force is in contact with the body receiving the force; the force disappears when contact is broken.
• Action-at-a-distance forces are interactions between objects that are not in contact, acting permanently with strength depending on the distance between objects.
• The closer the objects, the greater the force.

Gravitational Forces

• Gravity is the force with which all objects with mass attract each other.
• The greater the mass of the objects, the greater the gravitational pull.
• Gravity's effects are noticeable when at least one mass is very large, like a planet.
• Earth's attraction is huge, causing everything to tend to fall to its surface.

Decreased Gravity with Increased Distance

• As distance increases, the strength of gravitational forces decreases.
• The strength of the force decreases with the square of the distance.
• The distance between two objects considers the distance between their centers of mass.

Weight

• The weight of an object on Earth equals the pull of gravity exerted by Earth.
• Weight is a vertical force directed towards Earth's center, and its magnitude (W) equals m * g
• In formula W = m * g; m is mass, and g is 9.8 m/s², the acceleration of gravity on Earth’s surface.
• Weight is measured in newtons, and shouldn't confuse it with mass, measured in kg.
• The value of g depends on mass and radius of the celestial body.

Gravitational Fields

• An object with mass disturbs space, exerting a gravitational force on other masses entering the region.
• The disturbance created by mass in space is a gravitational field.
• Overlapping gravitational fields create a total gravitational field.

Planetary and Satellite Motions

• Planets orbit the Sun, and the Moon orbits Earth due to gravitational forces.
• Orbiting bodies are falling, but move so fast in a perpendicular direction to the gravitational force that they never crash.
• An orbit depends on speed and gravitational force.

Magnetic and Electric Forces

• Consist of at-a-distance forces that can be both attractive and repulsive.

Electric Forces

• Some materials can become electrically charged
• When two objects are charged, an electric force is created between them.
• Electric forces are repulsive if the charges are similar, and are attractive if opposite.

Magnetic Forces

• Magnets have magnetic properties, with north and south poles, interacting with magnets and metals (like iron) over a distance.
• Magnetic forces repel like poles and attract opposite poles.

Electric Charge

• Matter contains countless tiny electric charges, either positive or negative.

• Objects usually have an equal amount of + and - charges, cancelling each other out.

• An object with more of one type of charge has a net charge, becoming electrically charged.

• Positively charged objects contain more positive charges.

• Negatively charged objects contain more negative charges.

• Objects with zero net charge have an equal amount of positive and negative charges, being neutral.

• The greater the difference between positive and negative charges, the greater the magnitude of net charge.

• The magnitude of electric charge is measured in Coulombs (C).

Electrical Attraction and Repulsion

• Positively or negatively charged objects give rise to attraction and repulsion
• A charged object attracts neutral objects.
• Oppositely charged objects attract.
• Similarly charged objects repel.
• Neutral objects neither attract nor repel each other.
• Matter is generally electrically neutral.

Electric Field

• Electrically charged objects disturb space.
• A second charged object entering this disturbed region experiences an electric force.
• The disturbance created is called an electric field.
• Overlapping electric fields create a total electric field.