Physics Class: Understanding Speed, Velocity, and Acceleration

Physics: Speed, Velocity, and Acceleration

• Speed: a measure of how fast an object is moving; can be calculated using the formula: Speed = Distance / Time
• Units: important in speed calculations (e.g., meters per second, kilometers per hour)
• Example: a train moves at a constant speed of 90 km/h; how far does it travel in 4 hours? (Answer: 360 km)

Velocity

• Definition: displacement per unit of time; includes direction
• Formula: Velocity = Displacement / Time
• Examples:
  • A bird flies 150 meters east in 5 seconds; what is its velocity? (Answer: 30 m/s east)
  • A swimmer swims 200 meters east in 40 seconds; what is her velocity? (Answer: 5 m/s east)

Acceleration

• Definition: rate at which velocity changes over time; can be positive (speeding up) or negative (slowing down)
• Formula: Acceleration = Change in Velocity / Time
• Examples:
  • A plane decelerates from 200 m/s to 100 m/s in 10 seconds; what is its acceleration? (Answer: -10 m/s²)
  • A car increases its velocity from 20 m/s to 50 m/s in 10 seconds; what is its acceleration? (Answer: 3 m/s²)

Newton's Laws of Motion

• Newton's First Law of Motion: inertia; an object at rest will stay at rest, and an object in motion will stay in motion with the same speed and direction, unless acted upon by an external force

• Examples: a book sliding off a table, a car jerking forward when the brakes are suddenly applied, a ball rolling down a hill, a person sliding on ice, a coin spinning on a table

• Newton's Second Law of Motion: force acting on an object is equal to the mass of the object multiplied by its acceleration; F = ma

• Examples: a 10 kg object is accelerating at 5 m/s²; what is the force acting on it? (Answer: 50 N)

• Newton's Third Law of Motion: for every action, there is an equal and opposite reaction

• Examples: rowing a boat, a balloon rocket, jumping off a diving board

Net Force and Balanced vs Unbalanced Forces

• Net Force: the sum of all forces acting on an object; determines the object's acceleration and overall motion
• Calculating Net Force: add forces if they are in the same direction, subtract forces if they are in opposite directions
• Balanced Forces: when the forces acting on an object are equal in magnitude and opposite in direction; always equal to zero
• Unbalanced Forces: when the forces acting on an object are not equal in magnitude or not opposite in direction
• Example: two forces of 25 N and 25 N acting in opposite directions; the net force is 0 N, indicating balanced forces.