Chapter 9: Motion and Forces

• Section 1: Describing Motion– Motion– Reference point– Distance– Displacement– Vector

• Section 2:• Speed and Velocity– Speed– Average speed– Instantaneous speed– Velocity– Slope

Chapter 9: Motion and Forces

• Section 3: Acceleration– Acceleration

• Section 4:• Energy– Work– Energy– Kinetic energy– Potential energy– Gravitational potential energy– Elastic potential energy– Mechanical energy– Law of conservation of energy

Describing Motion

• Motion happens when the distance from one object to another changes.

Describing Motion

• A Reference Point is a place or object used for comparison to determine if something is moving

• Motion is different for different reference points The choice of reference point determines an object’s relative motion.

Describing Motion

• Displacement is the length and direction that an object has moved from its starting point.

• Distance is the total length of the path between two points.

• Displacement is a vector, which is a quantity that has both magnitude (size) and direction.

Examples of Relative Motion

• #1 • Train is moving 100kph relative to the tree/earth

• Passenger is running 15kph towards the back of the train.

• How fast is the runner moving toward the tree?Direction of Train

TreeDirection

of passenger

Examples of Relative Motion

• #2 • Train is moving 100kph relative to the tree/earth

• Passenger is running 20kph towards the front of the train.

• How fast is the runner moving toward the tree?

Direction of Train

TreeDirection

of passenger

Examples of Relative Motion

• #3 • Train is moving 10kph relative to the tree/earth

• Passenger is running 20kph towards the front of the train.

• How fast is the runner moving from the tree?

Direction of Train

TreeDirection

of passenger

Examples of Relative Motion

• #4 • Train is moving 10kph relative to the tree/earth

• Passenger is running 10kph towards the back of the train.

• How fast is the runner moving toward the tree?

Direction of Train

TreeDirection

of passenger