Physics Chapter 11: Motion and Distance

Describing Motion

• To describe motion completely, we need to know the distance, displacement, speed, velocity, and acceleration of an object.
• The SI unit for distance is meters (m), and other units that can be used include kilometers (km), centimeters (cm), and miles (mi).
• Distance and displacement are different, with distance being the total length of the path traveled and displacement being the shortest distance between the initial and final positions.
• Displacement is a vector quantity, and adding displacements requires the use of vector addition.
• Pythagorean's theorem is used to find the magnitude of the resultant vector in vector addition.

Distance-Time Graphs

• The slope of a distance-time graph represents the speed of an object.
• A straight line with a positive or negative slope represents an object moving at a constant speed.
• A line that curves upward or downward represents an object undergoing acceleration or deceleration.
• A horizontal line represents an object at rest.

Speed and Velocity

• Instantaneous speed and average speed are different, with instantaneous speed being the speed at a particular instant and average speed being the total distance traveled divided by the time taken.
• The SI unit for speed is meters per second (m/s), and other units that can be used include kilometers per hour (km/h) and miles per hour (mi/h).
• Speed and velocity are different, with speed being a scalar quantity and velocity being a vector quantity.
• The average speed equation is used to find the average speed of an object over a certain time period.

Acceleration

• Acceleration is the rate of change of velocity, and it is measured in meters per second squared (m/s²).
• A speed-time graph indicates acceleration when the slope of the graph is not zero.
• Instantaneous acceleration is the acceleration at a particular instant.
• Acceleration can be negative, indicating a decrease in velocity.

Forces

• A force is a push or pull that affects the motion of an object.
• The four main types of friction are static friction, kinetic friction, rolling friction, and fluid friction.
• Gravity and air resistance are forces that affect the motion of a falling object, with gravity acting downward and air resistance acting upward.
• Newton's first law relates a change in motion to a zero net force.
• Newton's second law relates force, mass, and acceleration, with the equation F = ma.

Momentum

• Momentum is the product of an object's mass and velocity.
• Momentum is conserved, meaning that the total momentum of a closed system remains constant.
• Newton's third law of motion states that every action has an equal and opposite reaction.

Work and Energy

• A force does work when it causes an object to move through a distance.
• The SI unit for work is the joule (J).
• Work and energy are related, with work being the transfer of energy from one object to another.
• Power is the rate of doing work, and it is measured in watts (W).
• One horsepower is equal to 746 watts.
• Machines can do work through three ways: by changing the direction of the force, by changing the magnitude of the force, or by changing the distance over which the force is applied.

Simple Machines

• The six types of simple machines are levers, pulleys, wheels and axles, inclined planes, wedges, and screws.
• A lever is a type of machine that consists of a rigid bar pivoted at a fixed point.
• The mechanical advantage of a machine is determined by its ability to change the direction or magnitude of the force.
• Two or more simple machines make up a compound machine.

Energy

• Energy is the ability to do work, and it is measured in joules (J).
• Work and energy have the same units because they are related.
• Kinetic energy is the energy of motion, and it depends on the mass and velocity of an object.
• Potential energy is the energy of position or stored energy, and it depends on the mass and height of an object.
• The major forms of energy include thermal, kinetic, potential, electrical, chemical, and nuclear energy.
• Energy can be converted from one form to another, but it cannot be created or destroyed.
• The law of conservation of energy states that the total energy of a closed system remains constant.
• Energy conversion takes place when an object falls to earth, with potential energy being converted to kinetic energy.
• Mass and energy are related, with mass being converted to energy according to the equation E = mc².
• The major nonrenewable and renewable sources of energy include fossil fuels, nuclear energy, solar energy, wind energy, and hydro energy.
• Energy conservation is the practice of reducing energy consumption, and it is important because it helps to reduce the depletion of energy resources and mitigate environmental pollution.