Force and Motion

• Notes cover force, motion, energy, and power
• Units, laws, and key figures are included

Motion

• Defined as a change in position of an object over time
• Motion is determined by using a stationary reference point

Force

• Causes an object to move via a push or a pull
• Can have more than one force acting on an object at the same time - Measured in Newtons (N)
• The unit of force, derived from the International System of Units (SI)

Balanced Forces

• Occur when the net force equals zero, resulting in no motion

Unbalanced Forces

• The net force is greater than zero
• Present when motion exists
• Can change an object’s motion
• Will alter the speed or direction of an object already in motion
• Can act in the same or opposite direction

Isaac Newton

• Creator of the 3 Laws of Motion
• English mathematician, physicist, astronomer, theologian, and author
• Considered the most influential scientist
• Born on December 25, 1642, in England
• Died on March 20, 1727
• Described as a natural philosopher and a key figure in the scientific revolution

Newton’s 1st Law of Motion (Inertia)

• Objects at rest stay at rest, and objects in motion stay in motion with a steady speed
• Unless acted upon by an external force such as pushes or pulls

Newton’s 2nd Law of Motion (Acceleration)

• A force acting on an object changes its speed or direction, accelerating the object
• The bigger the force, the more the object accelerates
• Equations:
  • Force (F) = mass (m) x acceleration (a), measured in Newtons (N)
  • Acceleration (a) = Force (F) / mass (m), measured in m/s²
  • Mass (m) = Force (F) / acceleration (a), measured in kg

Newton’s 3rd Law of Motion (Action and Reaction)

• When a force acts on an object, an equal force (reaction) acts in the opposite direction
• Actions are equal and opposite

Inertia

• The tendency of objects to resist changes in motion
• Seatbelts are an example

Net Force

• Sum total of all forces acting on an object

Work

• Requires a force applied to an object, causing it to move
• Two conditions:
  • The object must move as force is applied
  • The direction of the object's motion is the same as the direction of the applied force
• Work done by an applied force is the product of the magnitude of the displacement multiplied by the component of the force parallel to the displacement

Displacement

• Measurement of the change in distance and direction of an object from its starting point
• Change in position
• Distance is total length traveled

Work Equations

• W = F x d
• F: Force applied
• D: Displacement
• SI unit: Newton-meter (Nm) or Joule (J)
• Named in honor of James Prescott Joule
• 1 Nm = force of 1 Newton moving an object through 1 meter in the same direction as the force

Analyzing Work Problems

• Know the direction of the force and motion relative to the force
• Determine if they are parallel or perpendicular
• Work can be positive or negative

Positive and Negative Work

• When force and displacement are in the same direction, work is positive
• Negative work occurs when the force has a component opposite to the displacement

Energy

• Capacity to do work
• Includes stored (potential) and working (kinetic) energy

Stored Energy

• Gravitational potential energy depends on height and mass
• Elastic potential energy involves stretching, compressing, or bending
• Chemical energy relates to food and fuel

Working Energy

• Involves kinetic (movement), heat, light, electrical, and sound (vibrations) energy

Kinetic Energy

• Energy of motion for moving objects

Kinetic Energy Values

• KE = 1/2 mv^2
  • KE = Kinetic Energy (J or joule)
  • V = velocity (m/s)
  • M = mass (kg)

Potential Energy

• The energy of an object above the ground, represents "stored energy"
• PE = mgh
  • PE = Potential Energy (J or joule)
  • M = mass (kg)
  • G = Gravitational Acceleration (m/s²)
  • H = height (m)

Work and Energy Relationship

• Positive work leads to an increase in kinetic energy
• Negative work results in a decrease in kinetic energy
• Zero work implies no change in kinetic energy

Power

• The rate at which energy is transferred or work is done
• P = W/t
  • P = Power
  • W = Work Done
  • T = Time Taken

Power Equations

• Power = Work/Time = Force x Displacement/Time
• Power = Force x Velocity

Units for Power

• The SI unit is Joules per second (J/s) or watts (W)
• 1 Joule/Second = 1 Watt
• 1000 watts = 1 kilowatt (kW)

James Watt

• A Scottish inventor and mechanical engineer revolutionizing industry in Great Britain
• Improved the Newcomen steam engine
• Defined horsepower, still used in the automotive industry, to measure engine power

Horsepower

• The amount of work a horse can do in one second
• One horsepower equals 746 watts

Marketing Horsepower

• Measured the output of an actual horse and told customers exactly how many horses his engines could replace