Section 1 – Pages Newton’s 1 st Law Chapter 11 Force and Newton’s Laws

Mass and Inertia The mass of an object affects how easy it is to change its motion. The mass of an object affects how easy it is to change its motion. –Recall that mass is the amount of matter in an object. –The tendency of an object to resist a change in motion is called inertia. –The inertia of an object increases as the object’s mass increases.

Momentum Just as increasing the mass of an object makes it harder to stop, so does increasing the speed or velocity of an object. Just as increasing the mass of an object makes it harder to stop, so does increasing the speed or velocity of an object. The momentum of an object is a measure of how hard it is to stop the object, and it depends on the object’s mass and velocity. The momentum of an object is a measure of how hard it is to stop the object, and it depends on the object’s mass and velocity. The symbol for momentum is p. The symbol for momentum is p. The units for momentum are kg ● m/s in the direction of the velocity. The units for momentum are kg ● m/s in the direction of the velocity.

Momentum The momentum of an object is the amount of motion! The momentum of an object is the amount of motion! Momentum of an object is = mass x velocity. Momentum of an object is = mass x velocity. So an object with a large mass moving at a high velocity will have a large amount of momentum. So an object with a large mass moving at a high velocity will have a large amount of momentum. Bullet Train – China 220 mph / 350 kph

Momentum (Practice Problems) A 10,000 kg train is traveling east at 15 m/s. Calculate the momentum of the train. A 10,000 kg train is traveling east at 15 m/s. Calculate the momentum of the train. p = m * v p = m * v p = 10,000 kg * 15 m/s East p = 10,000 kg * 15 m/s East p = 150,000 kg · m/s East p = 150,000 kg · m/s East What is the momentum of a car with a mass of 900 kg traveling north at 27 m/s? What is the momentum of a car with a mass of 900 kg traveling north at 27 m/s? p = m * v p = m * v p = 900 kg * 27 m/s North p = 900 kg * 27 m/s North p = 24,300 kg · m/s North p = 24,300 kg · m/s North

Law of Conservation of Momentum In any collision, momentum is transferred from one object to another. In any collision, momentum is transferred from one object to another. Example – Cue ball hits other billiard balls. Example – Cue ball hits other billiard balls. The Law of Conservation of Momentum states that the total momentum of the objects that interact do not change. The Law of Conservation of Momentum states that the total momentum of the objects that interact do not change. The quantity of momentum is the same before and after they interact. The quantity of momentum is the same before and after they interact.

FORCES The Nature of Force: The Nature of Force: –A force is a PUSH or a PULL that gives energy to an object. –EXAMPLES OF FORCES:

Combining Forces The combination of all the forces acting on an object is the net force. The combination of all the forces acting on an object is the net force. When these forces are unbalanced, this causes an object to start moving, stop moving or change direction. When these forces are unbalanced, this causes an object to start moving, stop moving or change direction. Unbalanced forces acting on an object will change the object’s motion. Unbalanced forces acting on an object will change the object’s motion.

Combining Forces Unbalanced Forces (change motion) Unbalanced Forces (change motion) –Two forces acting in the same direction combine by adding together.  EX - dogs pulling a sled team

Combining Forces Unbalanced Forces (change motion) Unbalanced Forces (change motion) –Two forces acting in opposite direction combine by subtraction. –If one force is greater than the other force, the overall force is in the direction of the greater force of the greater force Ex. – Pushing open a door.

Combining Forces Balanced Forces (no change in motion) Balanced Forces (no change in motion) – Equal forces acting on one object in opposite directions are called balanced forces. –Balanced forces acting on an object will NOT change the objects motion. the objects motion. Example – Pushing on a wall.

Explain the Example Unbalanced Forces in opposite direction (Push)

Explain the Example Balanced Forces in opposite directions (Pull)

Explain the Example Unbalanced Forces in same direction (Push) Tailwind

Balanced vs. Unbalanced Forces

Newton’s 1 st Law of Motion Newton’s 1 st Law of Motion states: Newton’s 1 st Law of Motion states: An object at rest will continue to stay at rest AND an object in motion will continue to stay in motion unless acted on by an outside force. Therefore, since inertia is the tendency of an object to resist motion….. Therefore, since inertia is the tendency of an object to resist motion….. Newton’s 1 st Law of Motion is also known as the Law of Inertia. Newton’s 1 st Law of Motion is also known as the Law of Inertia.

Newton’s 1 st Law of Motion Remember, the amount of inertia an object has depends on its mass. Remember, the amount of inertia an object has depends on its mass. The greater the mass of an object the greater the inertia. The greater the mass of an object the greater the inertia.

Which is easier to move? Which has more inertia?

FRICTION The force that opposes motion is known as friction. Friction is a force that acts to oppose sliding between two surfaces that are touching.

FRICTION Creates…… Rubbing your hands together creates friction TRY IT! What Happens? Friction creates heat! Apply more pressure to your hands, what does it do? Pressure increases the amount of friction! Now try rubbing only ONE FINGER along your palm? What happens to friction? A smaller surface area decreases friction!

Factors that affect friction Surface Area – As surface area increases between surfaces, so does friction (more rubbing = more friction). Texture – A rougher surface = greater friction. A smoother surface = less friction. Mass/Weight – The greater the mass or weight of an object, the more friction it will create. Fluids – Fluids reduce friction by preventing surfaces from coming into contact.

Galileo’s Ideas About Motion It is the force of friction that usually makes moving objects slow down and come to a stop. To keep objects moving, a force has to be applied to overcome the force of friction. If friction could be removed, an object in motion would continue to move with a constant velocity.

Different types of Friction There are a few different types of Friction: ––1––1. Static Friction ––2––2. Sliding Friction ––3––3. Rolling Friction ––4––4. Fluid Friction

STATIC FRICTION #1 STATIC FRICTION: – –Have you ever tried to push something HEAVY? – –The type of friction that prevents a stationary object from moving when a force is applied is static friction. (The object is still and you are trying to move it!)   The rougher the surface, the larger the surface area, or the greater the mass = MORE STATIC friction

Sliding and Rolling Friction #2 Sliding Friction – –When solid surfaces slide over one another #3 Rolling Friction – –When an object rolls over a surface (less force needed than sliding friction – WHY?) Example: Match striking a surface Example: Bicycle tire on sidewalk

Fluid Friction #4 Fluid Friction – –When an object moves through a liquid or a gas, the fluid reduces friction by preventing objects from coming into contact.

Why can Friction be useful? Slows things down! Without friction you could not – –Walk around Or – –Move around Or – –Drive a car Imagine playing basketball in your socks or walking with sneakers on ice! How can we reduce friction?

Newton’s 2 nd Law Chapter 11 – Section 2 Pages 316 – 322 in textbook

Newton’s 2 nd Law of Motion DESCRIBES…. DESCRIBES…. –The net force on an object is equal to the product of its acceleration and its mass.

One Equation…. The relationship between the quantities of force, mass, and acceleration can be written in one equation: The relationship between the quantities of force, mass, and acceleration can be written in one equation: Force = Mass x Acceleration OR F = ma

Compare and Contrast Which shopping cart will be easier to push/move? Which shopping cart will be easier to push/move? How do the shopping carts relate to Newton’s 2 nd Law? How do the shopping carts relate to Newton’s 2 nd Law? Answer: The empty shopping cart has less mass than the full shopping cart, therefore it will need a smaller force to accelerate it. Answer: The empty shopping cart has less mass than the full shopping cart, therefore it will need a smaller force to accelerate it.

Units: F = ma Mass units example: kg Mass units example: kg Acceleration units example: m/sec/sec Acceleration units example: m/sec/sec Force units: kg * m/sec/sec ???? What a mess! Force units: kg * m/sec/sec ???? What a mess! Force is measured in units called the Newton Force is measured in units called the Newton (or N for short!) 1N = 1 kg x 1 m / sec / sec 1N = 1 kg x 1 m / sec / sec –This equation says that one Newton equals the force required to accelerate one kilogram of mass at 1 meter per second per second!

Describe these pictures using Newton’s 2 nd Law. Picture #1 Picture #2 How can you increase the acceleration of the wagon in Picture #3? Picture #3 1.Increase the force 2.Decrease the mass!

Sample Problem #1 A bicycle has a mass of 40.0 kilograms. Suppose the bike accelerates at 1.0 m/s/s. Find the net force being exerted on the bicycle. A bicycle has a mass of 40.0 kilograms. Suppose the bike accelerates at 1.0 m/s/s. Find the net force being exerted on the bicycle. Step 1: F = ma Step 2: F = 40.0 kg x 1.0 m/s/s Step 3: F = 40.0 N

Sample Problem #2 A speedboat is pulling a 52,000 gram skier. The force causes her to accelerate at 2.0 m/s/s. Calculate the force. A speedboat is pulling a 52,000 gram skier. The force causes her to accelerate at 2.0 m/s/s. Calculate the force. F = ma F = ma F = 52.0 kg x 2.0 m/s/s F = 52.0 kg x 2.0 m/s/s F = kg m/s/s OR F = kg m/s/s OR F = N F = N F AM

Sample Problem #3 An object with a mass of 50 kg is pushed with a force of 150 Newtons. What is the objects acceleration? An object with a mass of 50 kg is pushed with a force of 150 Newtons. What is the objects acceleration? A = F/M A = F/M A = 150 kg m/s/s / 50 kg A = 150 kg m/s/s / 50 kg A = 3 m/s/s or 3 m/s 2 A = 3 m/s/s or 3 m/s 2 F AM

Sample Problem #4 What is the mass of an object that accelerates at a rate of 5 m/s 2 after a force of 100 N is applied to it? What is the mass of an object that accelerates at a rate of 5 m/s 2 after a force of 100 N is applied to it? M = F/A M = F/A M = 100 kg * m/s/s / 5 m/s/s M = 100 kg * m/s/s / 5 m/s/s M = 20 kg M = 20 kg F AM

GRAVITY! The force that pulls object’s to the center of the earth is known as gravity. The force that pulls object’s to the center of the earth is known as gravity. Gravity attracts objects towards each other. Gravity attracts objects towards each other. Gravitational force decreases as: Gravitational force decreases as: 1)Distance increase between objects 2)Masses of objects decrease.

Law of Universal Gravitation Gravity is everywhere in the universe! Gravity is everywhere in the universe! The Law of Universal Gravitation states that the force of gravity acts between all objects in the universe! The Law of Universal Gravitation states that the force of gravity acts between all objects in the universe!

Acceleration due to GRAVITY Acceleration on the Earth due to gravity is Acceleration on the Earth due to gravity is 9.8 meters/second/second This means: This means: –For every second an object falls, it’s velocity increases by 9.8 m/s!

Let’s figure it out……. TimeVelocity 1.0 second 9.8 meters/second 2.0 seconds 3.0 seconds 4.0 seconds A parachutist jumps from a plane. What is her acceleration due to gravity? Complete the below chart meters/second 29.4 meters/second 39.2 meters/second

Weight The weight of an object is the size of the gravitational force exerted on an object. The weight of an object is the size of the gravitational force exerted on an object. Since weight is a force, you can rewrite Newton’s second law of motion as W=ma. Since weight is a force, you can rewrite Newton’s second law of motion as W=ma. Since acceleration due to gravity = 9.8 m/s 2, you can rewrite the formula for weight as: Since acceleration due to gravity = 9.8 m/s 2, you can rewrite the formula for weight as: W = m * 9.8 m/s 2

Weight How much would a 50 kg person weigh on the surface of the earth? How much would a 50 kg person weigh on the surface of the earth? Force = Mass * Acceleration (due to gravity) Force = Mass * Acceleration (due to gravity) Force (Weight) = 50 kg * 9.8 m/s 2 Force (Weight) = 50 kg * 9.8 m/s 2 Force (Weight) = 490 kg * m/s 2 Force (Weight) = 490 kg * m/s 2 Force (Weight) = 490 Newtons Force (Weight) = 490 Newtons

Who Wins? Acorn or Leaf? Answer – AIR RESISTANCE Answer – AIR RESISTANCE Why does an oak leaf flutter straight to the ground yet an acorn will fall straight down?

Air Resistance Air resistance is a form of friction that acts to slow down any object moving in the air. Air resistance is a form of friction that acts to slow down any object moving in the air. Air resistance increases as: Air resistance increases as: 1.The Surface area of the object increases 2.The velocity of the object increases When the air resistance balances the force of gravity, the net force is zero, also called terminal velocity. When the air resistance balances the force of gravity, the net force is zero, also called terminal velocity. In a vacuum, where there is no air, all objects fall with the same acceleration! In a vacuum, where there is no air, all objects fall with the same acceleration!

Newton’s 3 rd Law Chapter 11 – Section 3 Pages 323 – 328 in textbook

Newton’s 3 rd Law Newton’s 3 rd Law states: Newton’s 3 rd Law states: For every action, there is an equal and opposite reaction. Examples of Newton’s Third Law: Examples of Newton’s Third Law:

Action – Reaction Force Pairs When one object exerts a force on another object, the second object exerts the same size force in an opposite direction. When one object exerts a force on another object, the second object exerts the same size force in an opposite direction. According to Newtons 3 rd Law, forces always act in equal but opposite pairs. According to Newtons 3 rd Law, forces always act in equal but opposite pairs. However, an equal force acting on a greater mass will result in a smaller acceleration. However, an equal force acting on a greater mass will result in a smaller acceleration. This further demonstrates Newton’s 2 nd Law of Motion.

Action – Reaction Force Pairs The forces exerted by two objects on each other are often called action-reaction force pair. The forces exerted by two objects on each other are often called action-reaction force pair. Either force can be considered the action force or the reaction force. Either force can be considered the action force or the reaction force. Action and reaction force pairs don’t cancel because they act on different objects. Action and reaction force pairs don’t cancel because they act on different objects.

Action – Reaction Force Pairs When you walk forward, you push backward on the ground. Your shoe pushes Earth backward, and Earth pushes your shoe forward. Earth has so much mass compared to you that it does not move noticeably when you push it If you step on something that has less mass than you do, like a skateboard, you can see it being pushed back.