Newton’s Laws of Motion and Universal Forces Unit 1 Physical Science HS Credit Mrs. Rubel

Newton’s Laws of Motion Begins Here!! Begins Here!!

Great Scientists Aristotle- Incorrectly said force was required to keep an object in constant motion Aristotle- Incorrectly said force was required to keep an object in constant motion Galileo- with no resistance objects would move indefinitely Galileo- with no resistance objects would move indefinitely Newton- based on Galileo’s findings he came up with his law’s of motion Newton- based on Galileo’s findings he came up with his law’s of motion

Newton’s 1 st Law of Motion AKA The Law of Inertia AKA The Law of Inertia Inertia- an objects tendency to resist Inertia- an objects tendency to resist changes in motion an object at rest will remain at rest, and an object in motion will remain in motion in the same direction at a constant velocity until acted on by another force. an object at rest will remain at rest, and an object in motion will remain in motion in the same direction at a constant velocity until acted on by another force. Remember: The greater the mass of an object the greater the inertia

Have you heard of the FORCE of gravity? Have you heard of the FORCE of gravity? Gravity: the force that pulls objects towards each other Gravity: the force that pulls objects towards each other Since gravity is a force it also obeys Newton’s second law Since gravity is a force it also obeys Newton’s second law F=ma F=ma With this experiment, Galileo proved Aristotle wrong Since objects fall at the same speed, their acceleration is the same. All objects accelerate at the rate. Here on Earth the rate is: A g =9.8 m/s 2 Or A g =32 ft/s 2 With this experiment, Apollo 15 astronauts proved Galileo right. (link to You Tube)

Weight and Mass Weight is the force of gravity acting on an object Weight is the force of gravity acting on an object Weight (N) = mass (g) x acceleration of gravity (m/s 2 ) Weight (N) = mass (g) x acceleration of gravity (m/s 2 ) Note: just a version of F=ma, F = mass x gravity Note: just a version of F=ma, F = mass x gravity FYI: FYI: 1 pound = Newtons 1 pound = Newtons so 1/4 lb is slightly more that 1 N so 1/4 lb is slightly more that 1 N so a 1/4 lb burger is a "Newton" burger so a 1/4 lb burger is a "Newton" burger

F=ma F=ma So, weight is a type of Force So, weight is a type of Force The formula for weight: Weight = mass x A g The formula for weight: Weight = mass x A g Since A g = 9.8 m/s 2 then Since A g = 9.8 m/s 2 then Weight = mass x 9.8 m/s 2 Weight = mass x 9.8 m/s 2 Newton’s 2 nd Law & Weight Remember: 1 newton = 0.22 pounds

Try This: A bicycle takes 8.0 seconds to accelerate at a constant rate from rest to a speed of 4.0 m/s. If the mass of the bicycle and rider together is 85 kg, what is the net force acting on the bicycle? (Hint: First calculate the acceleration.)

For every action there is an equal & opposite reaction. For every action there is an equal & opposite reaction. This means every time a force is applied in one direction an equal force is applied in the opposite direction. This means every time a force is applied in one direction an equal force is applied in the opposite direction. If an object is not in motion, then all forces acting on it are balanced and the net force is zero! If an object is not in motion, then all forces acting on it are balanced and the net force is zero! Newton’s 3 rd Law of Motion :

Action-Reaction Forces If you push against a wall it pushes back If you push against a wall it pushes back These forces can cause motion, like a swimmer These forces can cause motion, like a swimmer They do not cancel each other out, because they act on different objects. They do not cancel each other out, because they act on different objects. 2 ice skaters 2 ice skaters

Questions that make you go Hmmmmmmm…. 1. Why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars? 1. Why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars? When you pull up on the handlebars, the handlebars push down on you, and this force is transmitted to the pedals. When you pull up on the handlebars, the handlebars push down on you, and this force is transmitted to the pedals. 2. Lets say you are weighing yourself on a set of bathroom scales. You are standing next to the sink in the bathroom. If at the same time while you are standing on the scales you reach under the sink and pull up on the sink, will the scales register your weight to be more or less than what they would register if you didn't pull up on the sink? 2. Lets say you are weighing yourself on a set of bathroom scales. You are standing next to the sink in the bathroom. If at the same time while you are standing on the scales you reach under the sink and pull up on the sink, will the scales register your weight to be more or less than what they would register if you didn't pull up on the sink? the scales would register heavy. Since you are lifting up on the sink, the sink is pushing down on you with an equal but opposite force and this would be transmitted to the scales. the scales would register heavy. Since you are lifting up on the sink, the sink is pushing down on you with an equal but opposite force and this would be transmitted to the scales.

Hmmmmmm…. 3. Lets repeat the question in the situation above except that you push down on the top of the sink instead of pulling up on the bottom of the sink. What will your weight be this time compared to what it would be if you did not push down on the sink? 3. Lets repeat the question in the situation above except that you push down on the top of the sink instead of pulling up on the bottom of the sink. What will your weight be this time compared to what it would be if you did not push down on the sink? The scales would register lighter. Since you are pushing down on the sink it is pushing up on you with an equal force which tends to lift you up off the scales some and therefore they register light. The scales would register lighter. Since you are pushing down on the sink it is pushing up on you with an equal force which tends to lift you up off the scales some and therefore they register light.

By definition, a Force is a push or a pull. By definition, a Force is a push or a pull. Just like Velocity & Acceleration Forces have both magnitude and direction components Just like Velocity & Acceleration Forces have both magnitude and direction components

Natural Forces There are 3 large natural forces that exist on Earth: 1) Gravity 2) Friction 3) Air Resistance

Forces A force causes an object to move, accelerate, change speed, or direction A force causes an object to move, accelerate, change speed, or direction Forces are represented by: Forces are represented by: Arrows Arrows Direction Direction Strength Strength represented by the length of the arrow represented by the length of the arrow

Balanced & Unbalanced Forces Balanced forces – opposite and equal forces acting on the same object result in NO motion of the object Unbalanced forces – two or more forces of unequal strength or direction acting upon on an object Unbalanced forces – two or more forces of unequal strength or direction acting upon on an object results in motion of the object results in motion of the object

Balanced or Unbalanced Forces? balanced unbalanced

Force/Free body diagrams (to show forces) used to show the relative magnitude and direction of all forces acting upon an object in a given situation. used to show the relative magnitude and direction of all forces acting upon an object in a given situation. a special example of vector diagram a special example of vector diagram size of the arrow represents size of the arrow represents amount of force amount of force

Force / Free-body Diagrams direction of the arrow shows the direction which the force is acting direction of the arrow shows the direction which the force is acting each force arrow is labeled each force arrow is labeled The object is usually represented by a box. Force arrows are drawn from the center of the box outward in the direction which the force is acting. The object is usually represented by a box. Force arrows are drawn from the center of the box outward in the direction which the force is acting. cfm#1 (look at types of forces also) cfm#1 (look at types of forces also) cfm#1 cfm#1

Combining Forces Net force: All forces are added or subtracted to create one total force Net force: All forces are added or subtracted to create one total force If net force is Zero then there is no change in motion. If net force is Zero then there is no change in motion. If there is a net force there is an acceleration If there is a net force there is an acceleration

Force Problem What is the net force on an object being pulled toward the west with a force of 30N and another force pulling the object toward the east with a force of 75N? What is the net force on an object being pulled toward the west with a force of 30N and another force pulling the object toward the east with a force of 75N?

Friction All moving objects encounter friction All moving objects encounter friction Without it most motion would be impossible Without it most motion would be impossible 4 types, static, sliding, rolling, fluid 4 types, static, sliding, rolling, fluid

Static Friction The force that keeps an object from moving The force that keeps an object from moving It is the largest frictional force It is the largest frictional force Always opposite direction of the applied force Always opposite direction of the applied force Pushing a Car Pushing a Car Walking Walking

Sliding Friction Once the object is in motion it experiences sliding friction Once the object is in motion it experiences sliding friction Opposite direction from applied force Opposite direction from applied force Less than static friction so less force is needed to keep it in motion Less than static friction so less force is needed to keep it in motion

Rolling Friction As something rolls, the object and floor bend slightly. This bend causes rolling friction As something rolls, the object and floor bend slightly. This bend causes rolling friction It is a much smaller force than static friction It is a much smaller force than static friction As much as 1000 times smaller As much as 1000 times smaller Allows you to move heavy objects Allows you to move heavy objects Ball bearings reduce friction Ball bearings reduce friction

Fluid Friction It opposes the motion in the liquid or gas It opposes the motion in the liquid or gas Like swimming, it is hard to move Like swimming, it is hard to move If you are in the air, fluid friction is called air resistance If you are in the air, fluid friction is called air resistance At higher speeds it is very noticeable. At higher speeds it is very noticeable.

Force of Gravity A force that acts between 2 objects A force that acts between 2 objects an attractive force, pulls objects together an attractive force, pulls objects together causes objects to accelerate downward causes objects to accelerate downward Falling objects, gravity pulls down, What pushes up? Falling objects, gravity pulls down, What pushes up? air resistance acts in opposite direction air resistance acts in opposite direction Terminal Velocity- when Gravity and air resistance cancel each other out (velocity of falling body becomes constant) Terminal Velocity- when Gravity and air resistance cancel each other out (velocity of falling body becomes constant)

Terminal Velocity

Free Fall – Gravity Only Skydivers say they are in free fall, but that isn’t true. The only way to have free fall is when gravity is the only force working on you (no air resistance.) You can have free fall in a vacuum. Here’s the only example of a human being experiencing free fall to the Earth:

Projectile Motion When an object not only goes up and down but When an object not only goes up and down but It is a It is a Air resistance and gravity are the only forces acting on a projectile Air resistance and gravity are the only forces acting on a projectile What falls faster, an object that falls straight down, or one that has a horizontal velocity? What falls faster, an object that falls straight down, or one that has a horizontal velocity?

Forces Problems 1.Two tugboats are moving a barge. Tugboat A exerts a force of 3000 newtons on the barge. Tugboat B exerts a force of 5000 newtons in the same direction. What is the combined force on the barge? 1.Two tugboats are moving a barge. Tugboat A exerts a force of 3000 newtons on the barge. Tugboat B exerts a force of 5000 newtons in the same direction. What is the combined force on the barge? 2.Draw arrows showing the individual and combined forces of the tugboats in #1. 2.Draw arrows showing the individual and combined forces of the tugboats in #1.

Force Problems 3.Now suppose that Tugboat A exerts a force of 2000 newtons on the barge and Tugboat B exerts a force of 4000 newtons in the opposite direction. What is the net force on the barge? 3.Now suppose that Tugboat A exerts a force of 2000 newtons on the barge and Tugboat B exerts a force of 4000 newtons in the opposite direction. What is the net force on the barge? 4.Draw arrows showing the individual and combined forces of the tugboats in #3. 4.Draw arrows showing the individual and combined forces of the tugboats in #3.

Force Problem 5.Could there ever be a case when Tugboat A and Tugboat B are both exerting a force on the barge but the barge doesn't move? Draw arrows showing the individual and combined forces in such a situation. 5.Could there ever be a case when Tugboat A and Tugboat B are both exerting a force on the barge but the barge doesn't move? Draw arrows showing the individual and combined forces in such a situation.

Universal Forces Forces that can be found anywhere in the universe

Electromagnetic Force Electric and Magnetic Forces are the only forces that can both attract and repel Electric and Magnetic Forces are the only forces that can both attract and repel Electric forces- between charged particle, positive attracted to negative Electric forces- between charged particle, positive attracted to negative Clothes in a dryer Clothes in a dryer Magnetic forces- N and S poles, opposites attract, likes repel Magnetic forces- N and S poles, opposites attract, likes repel

Nuclear Forces Two forces a strong and a weak force hold an atom together Two forces a strong and a weak force hold an atom together The strong nuclear force overcomes the protons repulsion force The strong nuclear force overcomes the protons repulsion force This force is over 100x stronger than electric forces This force is over 100x stronger than electric forces The weak force is involved in radioactive processes The weak force is involved in radioactive processes

Fusion vs Fission (see page 113) In nuclear fission, a small amount of mass is converted into large amounts of energy. The nuclei of atoms are broken apart. Nuclear power plants used this energy to generate electrical energy. In nuclear fusion, a small amount of mass becomes much larger when nuclei of atoms combine. An example would be the Sun, when hydrogen atoms combine to become larger helium atoms.

Gravitational Force Attractive force between any two masses Attractive force between any two masses This force is very small compared to all the rest This force is very small compared to all the rest Newton came of with the Law of Universal Gravitation, which explains how we can find the gravitational force of any object Newton came of with the Law of Universal Gravitation, which explains how we can find the gravitational force of any object A large mass is required for gravity to be felt A large mass is required for gravity to be felt

Gravity is relational to distance and mass The further apart two objects are the less the gravitational force The further apart two objects are the less the gravitational force The smaller the masses, the less gravitational force. The smaller the masses, the less gravitational force. Gravity still has pull over millions and millions of miles apart Gravity still has pull over millions and millions of miles apart As distance doubles the force gets quartered As distance doubles the force gets quartered

The Earth Moon System The moon stays in orbit because of Earth’s gravity The moon stays in orbit because of Earth’s gravity It works very similar to a centripetal force It works very similar to a centripetal force It pulls in on an object It pulls in on an object So as the moon follows this circular path, it’s gravitational force has an affect of Earth. So as the moon follows this circular path, it’s gravitational force has an affect of Earth.

Satellites Satellites stay in orbit with centripetal force of gravity Satellites stay in orbit with centripetal force of gravity If it were to slow down it would lose altitude If it were to slow down it would lose altitude Satellite motion requires energy for the satellite to move forward, while orbiting due to the centripetal force of gravity. Satellite motion requires energy for the satellite to move forward, while orbiting due to the centripetal force of gravity.