Introduction to Physics: Motion, Forces, and Energy
1. Systems of Reference and Movement Characteristics
System of Reference
Any definite point from where we observe the position of a moving object over a period of time.
Characteristics of Movement
- Position (x): The place an object occupies with respect to the origin (O) of the chosen system of reference.
- Trajectory: The line connecting all the points corresponding to the different positions of a moving object over a period of time.
2. Speed and Acceleration
Speed
The physical magnitude that represents distance traveled per unit of time.
Acceleration
The rate of change of speed. Average acceleration (am) is calculated by dividing the variation of speed (Δv) by the time spent at this variation (Δt).
Types of Movement
- Based on Trajectory:
- Rectilinear: Movement along a straight line.
- Curvilinear: Movement along a curve.
- Based on Speed:
- Uniform: Constant speed (v=cte), meaning no acceleration (a=0).
- Accelerated: Non-constant speed (a≠0).
3. ULM Equation and Forces
ULM (Uniform Linear Motion)
A body has uniform linear motion if its trajectory is a straight line and its speed is constant.
Force
The direct cause of changes in speed and deformation a body can experience. Force is a vector magnitude, represented by an arrow indicating direction and magnitude (length).
Types of Forces
- Contact Forces: Forces between bodies in direct contact.
- Forces at a Distance: Forces between bodies not in direct contact.
Effects of Forces
- Variation in State of Motion: Changes in a body’s state of motion (rest or movement) according to Newton’s law: F=m·a (Force = mass x acceleration).
- Deformations: Alterations in the shape of bodies, categorized by the body’s response:
- Elastic Bodies: Return to their original shape after the force is removed.
- Plastic (Malleable) Bodies: Permanently deform under force.
- Rigid (Hard) Bodies: Resist deformation.
4. Gravitational Interaction and Weight
Gravitational Interaction
An attractive force between objects with mass. Its intensity decreases with increasing distance.
Weight of Bodies
The force exerted by the Earth on a body, measured in Newtons (N).
Weight and Mass
- Weight (P): The gravitational force acting on a body.
- Mass (m): A measure of the amount of matter in a body.
The relationship between weight, mass, and acceleration due to gravity (g) is: P=m·g
5. Archimedes’ Principle and Buoyancy
Archimedes’ Principle
A body submerged in a liquid or gas experiences an upward force (upthrust, E) equal to the weight of the fluid displaced.
Factors Affecting Buoyancy
- Volume of Submerged Solid: Larger submerged volume displaces more fluid, resulting in greater upthrust.
- Density of the Liquid: Denser liquids exert greater upthrust.
Apparent Weight
The difference between a body’s real weight (P) and the upthrust (E) it experiences when submerged: P’=P-E
6. Energy and its Forms
Energy
The ability of a system to produce changes in itself or other systems. Measured in Joules (J). Energy is conserved, meaning it can be transformed but not created or destroyed.
Mechanical Energy (Em)
The sum of kinetic and potential energy: Em = Ek + Ep
Kinetic Energy (Ek)
Energy possessed by a body due to its motion: Ek = 1/2·m·v² (where m is mass and v is velocity)
Gravitational Potential Energy (Ep)
Energy possessed by a body due to its position in a gravitational field: Ep = m·g·h (where m is mass, g is acceleration due to gravity, and h is height)
Work of a Force
The energy transferred to an object when a force causes displacement: W = F·d (where F is force and d is displacement)
7. Temperature and Heat Transfer
Temperature
A measure of the average kinetic energy of the particles within a substance.
Heat Transferred
- Conduction: Heat transfer through direct contact in solids, without matter transport.
- Convection: Heat transfer in fluids through the movement of matter (convection currents).
- Radiation: Heat transfer through electromagnetic waves, requiring no medium. Can occur in a vacuum or through matter like air.