Newton s Laws of Motion and Universal Forces

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

2. Newton�s Laws of Motion Begins Here!!

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

4. Newton�s 1st Law of Motion AKA The Law of Inertia 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.

5. Have you heard of the FORCE of gravity? Gravity: the force that pulls objects towards each other Since gravity is a force it also obeys Newton�s second law F=ma

6. Weight and Mass Weight is the force of gravity acting on an object Weight (N) = mass (g) x acceleration of gravity (m/s2) Note: just a version of F=ma, F = mass x gravity FYI: 1 pound = 4.448 Newtons so 1/4 lb is slightly more that 1 N so a 1/4 lb burger is a "Newton" burger

7. F=ma So, weight is a type of Force The formula for weight: Weight = mass x Ag Since Ag= 9.8 m/s2 then Weight = mass x 9.8 m/s2 Newton�s 2nd Law & Weight

8. 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.)

9. 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. If an object is not in motion, then all forces acting on it are balanced and the net force is zero! Newton�s 3rd Law of Motion:

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

11. 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? 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? 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.

12. 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? 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.

13. By definition, a Force is a push or a pull.

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

15. 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 results in motion of the object

16. Balanced or Unbalanced Forces?

17. 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. a special example of vector diagram size of the arrow represents amount of force

18. Force / Free-body Diagrams direction of the arrow shows the direction which the force is acting 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. http://www.physicsclassroom.com/Class/newtlaws/u2l2c.cfm#1 (look at types of forces also)

19. Combining Forces 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 there is a net force there is an acceleration

20. 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?

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

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

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

24. 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 As much as 1000 times smaller Allows you to move heavy objects Ball bearings reduce friction

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

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

27. Terminal Velocity

28. Projectile Motion When an object not only goes up and down but It is a 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?

29. May the forces be with you and not against you!!

30. 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? 2.Draw arrows showing the individual and combined forces of the tugboats in #1.

31. 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 combined force on the barge? 4.Draw arrows showing the individual and combined forces of the tugboats in #3.

32. 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.

33. Universal Forces Forces that can be found anywhere in the universe

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

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

36. 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.

37. Gravitational Force Attractive force between any two masses 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 A large mass is required for gravity to be felt

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

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

40. Satellites Satellites stay in orbit with centripetal force of gravity 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.