Warm Up – Copy these definitions down in your notebook Warm Up – Copy these definitions down in your notebook. Leave space in between each one for more notes. An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. For every action, there is an equal and opposite reaction.

Newton’s Laws of Motion & Forces

Regarding Motion, Newton says: “In order to move an object with mass, you need to apply a force” The greater the mass = The greater inertia => more force is needed

Force Force – push or pull and causes things to accelerate 1000 kg

Balanced vs. Unbalanced Forces Balanced Forces – The net force on an object is zero so no acceleration in any direction Unbalanced Forces – The net force on an object is greater than zero causing acceleration in a direction

First Law of Motion Inertia – The tendency of an object to resist a change in motion; resist a push/pull (force) Newton’s 1st Law of Motion: once in motion an object stays in motion - unless acted upon by an outside force An object at rest stays at rest – unless acted upon by an outside force

Newton’s First Law and You Because of inertia, objects (including you) resist changes in their motion. When the car going 80 m/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.

Second Law of Motion Force = mass  acceleration (F = m  a) Acceleration depends on the object’s mass and the force acting on the object More Force = More Acceleration More Mass = Less Acceleration

Second Law of Motion If you apply more force to an object, it accelerates at a higher rate

Second Law of Motion If the same force is applied to an object with greater mass, the object accelerates at a slower rate because mass adds inertia

Second Law of Motion

Third Law of Motion For every action there is a reaction equal in magnitude but opposite in direction. Upwards motion Downwards force

Third Law of Motion

Balanced vs. Unbalanced Forces Balanced Forces – The net force on an object is zero so no acceleration in any direction Unbalanced Forces – The net force on an object is greater than zero causing acceleration in a direction

Take Notes on this Video

Forces will cancel each other and produce NO ACCELERATION! Balanced Forces Object 5 N 5 N Equal Pushing Forces will cancel each other and produce NO ACCELERATION!

Balanced Forces If these football players push on each other equally as hard, will either one move?

Balanced Forces Gravity pulls down on you, the ground pushes back up, KEEPING YOU WHERE YOU ARE!

Forces will not cancel each other out and produce ACCELERATION! Unbalanced Forces Object 10 N 5 N Not Equal Pushing Forces will not cancel each other out and produce ACCELERATION!

What is the net force and in what direction? Net Forces Object 10 N 5 N What is the net force and in what direction? (10 N) – (5 N) = 5 N to the right

What is the net force and in what direction? Net Forces Object 20 N 5 N What is the net force and in what direction? (20 N) + (5 N) = 25 N to the right

What is the net force and in what direction? Net Forces Object 15 N 30 N What is the net force and in what direction? (30 N) – (15 N) = 15 N to the left

What is the net force and in what direction? Net Forces Object 10 N 10 N What is the net force and in what direction? (10 N) – (10 N) = 0 N

F m a Second Law of Motion A car rolls down a ramp with a force of 2 newtons. The car has a mass of 0.5 kg. What is the acceleration of the car? F = m  a (2 N)  (0.5 kg) = 4 m/s2 F m a

and Free Fall

Gravity Gravity – g; acceleration caused by attraction between objects with mass Gives weight Causes free fall

Weight Fw = mg Weight – force caused by gravity’s pull measured in N depends on mass, gravity, and location weight is less on the moon due to less gravity Weight Gravity Mass

Mass Mass (amount of matter) measured in kg does NOT depend on gravity or location mass is the same everywhere in the universe

Gravity on earth = 9.8 m/s2 Gravity on the moon = 1.6 m/s2 Fw = mg The weight of 1 kg object ON EARTH (1 kg)(9.8 m/s2) = 9.8 N The weight of 1 kg object ON THE MOON (1 kg)(1.6 m/s2) = 1.6 N

Practice Unless the problem says otherwise, assume you are on Earth, where g = 9.8 m/s2 What is the weight of a 100 kg person? (100 kg) x (9.8 m/s2) = 980 N What is the mass of a rock that weighs 196 N? (196 N) ÷ (9.8 m/s2) = 20 kg

What’s your weight on Mars? Calculate and compare the weight of a 100 kg person on Earth and on Mars. (g = 3.7 m/s2 on Mars) Earth = (100 kg) × (9.8 m/s2) = 980 N Mars = (100 kg) × (3.7 m/s2) = 370 N The MASS did NOT change!!!

Free Fall Free Fall – when gravitational pull is the only force acting on an object Falling objects speed up 9.8 m/s2 for every second they fall Time Speed 1 9.8 2 19.6 3 29.4 4 39.2 5 49

Practice The force of gravity on the surface of Mercury is much less than on Earth. A rock has a weight of 100 N on Earth. What do you know about the weight of the rock on Mercury? The rock will weigh exactly 100 N The rock will weigh more than 100 N The rock will weigh less than 100 N There is not enough information

Practice A chair has a mass of 10 kilograms on Earth. What is the mass of the chair on Mercury? Exactly 10 kg More than 10 kg Less than 10 kg Not enough information

Practice If an astronaut, with a mass of 90 kg, has a weight of 145.8 N on the Moon, what is the value of the Moon’s gravitational acceleration? (145.8 N) ÷ (90 kg) = 1.62 m/s2