Understanding Forces and Motion

• A force is a push or pull that can cause an object to move, stop, or change direction.

• In physics, a force accelerates objects.

• A stationary object will not move without a force acting on it.

• Forces can be applied in the same or opposite directions.

• An object can have multiple forces applied to it simultaneously.

• The net force is of interest, and it is the combination of all forces acting on an object.

• The unit for measuring force is the Newton (N), named after Isaac Newton.

• Forces come in pairs and have both magnitude and direction.

• Force is a vector quantity.

• Example: 5N, north (up) refers to a magnitude of 5N with an upward direction.

• Effects of push and pull forces:

• A force can make a stationary object move.

• A force can stop a moving object.

• A force can make an object move slower or faster.

• A force can change the direction of a moving object.

• Net Force

• The overall force acting on an object after all forces are combined.

• Forces in the same direction are added together.

• Forces in opposite directions are subtracted.

• Force should always include magnitude and direction.

• To calculate net force, add forces in the same direction.

• To calculate net force, subtract forces in opposite directions.

Types of Forces: Contact Forces

• Contact forces occur when interacting objects are physically touching each other.
• Friction force opposes the motion of objects that touch and move past each other.
• Normal force is a perpendicular force with which two objects push each other to prevent solid objects from passing through.
• Applied force occurs when a force is applied to something by a person or object.

Types of Forces: Non-Contact Forces

• Non-contact forces influence objects without physical contact.
• Types: Electromagnetic, gravity, and nuclear forces.
• Electromagnetic force combines magnetic fields and electrical interactions between charged particles.
• Gravity is a force that acts between any two masses.
• Nuclear force holds protons and neutrons within the nucleus.
• Weak nuclear force is responsible for radioactive decay, breaking down heavy atomic particles and releasing energy.
• Strong nuclear force acts only on hadrons (protons and neutrons inside the nucleus).

Friction

• Occurs when two surfaces slide or attempt to slide against each other.
• It slows down movement and acts in the opposite direction to the object's motion.
• Friction is a type of force that affects how things move.
• Friction is useful sometimes, such as preventing cars from skidding, keeping hands warm, and helping to grip objects.
• Less friction is desired when moving faster:
• Ice skaters use narrow blades to reduce friction.
• Olympic cyclists utilize narrow tires with few ridges to minimize friction and increase speed.

Types of Friction

• Static friction acts on objects that are not moving and opposes the applied force.
• Sliding friction opposes the motion of an object as it slides over a surface and occurs when objects rub or slide against each other.
• Rolling friction acts on rolling objects and occurs when a body rolls over another body's surface.
• Fluid friction opposes the motion of an object through a fluid and occurs between fluid layers moving relative to each other.

Applied and Normal forces

• Applied force
• A perpendicular force with which two objects push each other.
• The force that surfaces exert to prevent solid objects from passing through each other.
• Support force exerted on an object which is in contact with another.
• Normal force
• A perpendicular force with which two objects push each other.
• The force that surfaces exert to prevent solid objects from passing through each other.
• Support force exerted on an object which is in contact with another.

Four Fundamental Forces of Nature

• Strong force binds the nucleus.
• Electromagnetic force binds atoms.
• Weak force is involved in radioactive decay.
• Gravitational force binds the solar system.

Non-Contact Forces Explained

• Gravity
• Force between any two objects and is an attractive force due to their masses.
• Gravitational force is directly proportional to the product of the masses and inversely proportional to the square of the distance between them.
• Both gravity and air resistance affect the motion of a falling object.
• As objects fall, they accelerate.
• Gravity is always equal to the object's weight (W=mg), always attractive, and never repulsive.
• Electromagnetism
• Is more than a billion times stronger than gravity and combines magnetic and electrical fields between charged particles (positive and negative)/(protons and electrons).
• Unlike charges attract, and like charges repel each other.
• Works at an infinite range.
• Nuclear Force
• Prevents the mutual repulsion between positively charged protons.
• The strong force binds nuclear particles tightly; when lightweight elements fuse, it is called nuclear fusion releasing substantial energy.
• A tremendous amount of energy is released when heavy nuclei are broken apart, called nuclear fission.
• Weak nuclear forces are responsible for radioactive decay. This type helps generate sunlight and allows for medical diagnoses and treatment.

Strong Force

• Acts only on hadrons (protons and neutrons inside the nucleus).
• It is the strongest of all the basic forces of nature.
• Shortest range, of the order of 10^-15 m.
• Holds protons and neutrons together.

Weak Force

• Significant in nuclear processes, such as the beta-decay of certain nuclei.