Chapter 2 Newtons First Law of Motion Law

Chapter 2 Newton’s First Law of Motion- Law of Inertia

2. 1 Aristotle’s classification of Motion A force is a push or pull

Aristotle Most famous scientist, philosopher and educator in ancient Greece. Classified motion into two types: natural and unnatural

2 Types of Motion Natural Motion: Directed up or down Objects have resting places Heavy objects fall faster than light objects Occurs without force Unnatural motion: requires forces

2. 2 Galileo’s Concept of inertia Disputed Aristotle that heavier objects fall faster than lighter objects. Disputed Aristotle that a force is required to keep an object moving.

2. 2 Galileo’s Concept of inertia Galileo said: A force was required to start an object moving No force was required to keep it moving except to overcome friction When friction is absent, a moving object does not need a force to keep moving

2. 2 Galileo’s Concept of inertia Inertia: the property of motion- the tendency of objects is to remain as they are (if they are moving, they remain moving; if they are at rest, they remain at rest)

Question • Distinguish between Aristotle and Galileos’ concepts of motion

2. 3 Galileo formulated the concepts of speed and velocity Speed: the distance covered per unit time speed= distance/time average speed: total distance divided by total time instantaneous speed: speed at any instant constant speed: movement at a fixed distance over time ratio (steady speed)

Speed • Speed = Distance/Time • Therefore: • Distance = ? • Time = ?

2. 3 Galileo formulated the concepts of speed and velocity Bowling Ball: 12 mi/hr = 20 km/hr = 6 m/s Tsunami: 50 mi/hr = 80 km/hr = 22 m/s Sprinting Cheetah: 62 mi/hr = 100 km/hr = 28 m/s

2. 3 Galileo formulated the concepts of speed and velocity Velocity: the speed of an object and the specific direction it is headed in vector quantity: a quantity that specifies direction as well as magnitude constant velocity: constant speed and constant direction

Question #1? What is the average speed of a cheetah that sprints 100 m in 4 s? 100 m / 4 s = 25 m/s

Question #2? ? The speedometer on a bicycle moving east reads 50 km/hr. It passes another bicycle moving west at 50 km/hr. Do both bikes have the same speed? Do they have the same velocity?

Question #3? ? ? • • A car is travelling at 75 km/hr for 3. 2 hours. How far does it travel? A runner is running at 9 km/hour and runs 15 km. How long is she running for?

2. 4 Motion is relative Everything is always moving You are moving relative to the sun and stars You are at rest relative to the Earth Motion is measured against a frame of reference (usually the surface of the Earth)

2. 4 Motion is relative When you are walking at a speed of 1 m/s down the aisle of a train, your speed relative to the floor of the train is 1 m/s. The floor of the train is your ______? _______.

2. 4 Motion is relative If you change your FRAME OF REFERENCE to the ground, your relative speed would change. HOW? ? ?

2. 4 Motion is relative Suppose the train is traveling at a speed of 50 m/s and it is traveling East. a. What would your speed be if you were also walking in a direction east down the aisle? b. What would your relative speed be if you were walking in a direction WEST down the aisle?

2. 5 Newton’s first law of motion- law of inertia Newton’s 1 st Law of Motion: Every object continues in a state of rest, or in a state of motion in a straight line at a constant speed, unless it is compelled to change that state by forces exerted upon it.

2. 6 Net Force/ 2. 8 support force Net Force (∑f) is the combination of all forces acting upon an object Measured in Newton (N) 1 Newton (1 N) is equal to the force required for a 1 kg object to accelerate 1 m/s

2. 6 Net Force/ 2. 8 support force Other Forces (also measured in Newtons) Normal or support force (FN) is the force that acts at a right angle to the surface (upward (+) or downward (-)) Frictional force (Ff) Tension force (Ft) is the force exerted by a string, cable, chain, or similar object on another object Force of gravity (g or Fw) ~ 9. 8 m/s

2. 7 Equilibrium for objects at rest All objects at rest are in equilibrium When the net force is zero, that object is in mechanical equilibrium Force Diagrams: show all forces acting on an object

2. 9 Equilibrium for moving objects Equilibrium is a state of no change Objects at rest are in static equilibrium Objects in motion are in dynamic equilibrium

2. 10 The earth moves around the sun We live on a moving Earth We do notice this because we are moving at the same speed If we flip a coin in the air while flying in an airplane, the coin will behave as if the airplane were at rest. In other words, the coin will keep-up with you!