1 / 31

Sir Isaac Newton

Sir Isaac Newton. 1 st and 2 nd laws of motion. Sir Isaac Newton. Newton made many contributions to science. He developed the scientific method. You can thank him for calculus. His biggest contribution was developing laws of forces and gravity.

wrigleyr
Download Presentation

Sir Isaac Newton

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Sir Isaac Newton 1st and 2nd laws of motion

  2. Sir Isaac Newton • Newton made many contributions to science. • He developed the scientific method. • You can thank him for calculus. • His biggest contribution was developing laws of forces and gravity. • Born in England in 1642 to a poor farming family. • He studied math, physics, astronomy • Knighted by Queen Anne in 1705 • He never married • Died in 1727 at age 84 • Buried in Westminster Abby

  3. Sir Isaac Newton • There is a famous myth about Newton that many of you many have heard. • He was sitting in his garden when an apple fell on his head. Right then and there he discovered gravity along with the other forces. • It is doubtful this really happened but it’s a good story. • It was his understanding of math that ultimately allowed him to determine the three laws of motion for the universe.

  4. Newton’s First Law • An object at rest will stay at rest and an object in motion will stay in motion unless it is acted upon by an unbalanced force. • An object tends to stay “doing what it is doing” unless another force changes that. • Water in a cup that is sitting in the cup holder of the car. • What happens to you in the car when it comes to an abrupt stop? • Why do cars have head rests?

  5. 1st Law • Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless. • mass = inertia • mass = inertia These pumpkins will not move unless acted on by an unbalanced force.

  6. Force • Force- - A force is a push or pull on an object • This happens when an object interactswith another object

  7. Balanced and Unbalanced Forces • Balanced Forces- Forces on an object are equal in size and opposite in direction. The object does not accelerate. • Unbalanced forces- Forces on an object that are unequal in size and in the opposite direction. The object accelerates in the direction of the larger force.

  8. Activity- With a partner, apply a set of balanced forces on a book. What happens to the book? • Now apply a set of unbalanced forces to make the book accelerate to the right. How many ways can you achieve this? Explain.

  9. Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force? It’s a force we sometimes cannot see –

  10. Friction…. Objects on earth, unlike the frictionless space the moon travels through, are under the influence of friction.

  11. What is this unbalanced force that acts on an object in motion? Friction! • There are four main types of friction: • Sliding friction: ice skating • Rolling friction: bowling • Fluid friction (air or liquid): air or water resistance • Static friction: initial friction when moving an object

  12. Slide a book across a table and watch it slide to a rest position. The book comes to a rest because of the presence of a force - that force being the force of friction - which brings the book to a rest position.

  13. In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top.)

  14. Free Body Diagrams • Shows all forces acting on an object • Abbreviations to know: app = push or pull; norm = normal (floor, ground, chair, table); frict= friction; grav= gravity

  15. Newtons’s 1st Law and You Don’t let this be you. Wear seat belts. Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.

  16. The End For today….

  17. Newton’s 2nd Law F = ma

  18. Newton’s 2nd Law • The net force acting on an object causes the object to accelerate in the direction of that net force. • It explains how the velocity of an object changes when an external force acts on it. • The net force of an object is equal to the product of its mass and acceleration • F=ma (Force = mass x acceleration)

  19. SI Units • F = Force in Newtons (N) • The unit kg × m/s2 is called a Newton • m = Mass in kilograms (kg) • a = Acceleration in (m/s2)

  20. Newton’s 2ndLaw (F = ma) • How much force is needed to accelerate a 1400 kilogram car 2 m/s2? • Write the formula • F = ma • Fill in given numbers and units • F = 1400 kg x 2 meters per second/second • Solve for the unknown • 2800 kg * meters/second2 or2800 N

  21. Practice problems • If 12N net force is applied to a 3 kg object, what is the acceleration? (write formula, show substitution with units, write answer with correct units) • Rearrange the formula F=ma • a=F/m (force divided by mass) • a= 12N / 3kg • a= 4 m/s2

  22. A force of 15 N is exerted on a book causing it to accelerate 5 m/s2, what is the mass. (show work) • Rearrange the formula F=ma • m=F / a (force divided by acceleration) • m=15N / 5 m/s2 • m= 3 kg

  23. Gravity • Anything that has mass is attracted by the force of gravity. • Law of Gravitation • Any two masses exert an attractive force on each other. • The attractive force depends on the mass of the two objects and the distance between them.

  24. Gravity • Gravity increases as the mass of either object increases. • Gravity decreases as the distance between the two objects increases. • You can’t feel the gravitation pull of the desk on you because it doesn’t have enough mass. • You can feel the gravitational attraction of the earth because it is close enough and has a large mass.

  25. Gravitational Acceleration of Earth • Near the Earth’s surface, the gravitational acceleration is 9.8 m/s2 • You can round this to 10.0 m/s2 • The force of Earth’s gravity is always down. • All objects fall at the same acceleration no matter how large or small they are.

  26. Weight • Standing here, my acceleration is zero and the net force on me is zero. • The Earth is still pulling me down but the floor is pushing me up with the same force. I’ll try not to fall.  • Weight is the gravitational force on an object. Weight = mass x acceleration due to gravity (W=mg) W = m x 9.8 m/s2 (or 10.0 m/s2) metric units are in Newtons

  27. Weight vs Mass • Remember: Mass is the amount of matter in an object • The difference? • Mass can’t change, weight can change with gravity.

  28. What is the weight of a 70 kg person? (write formula, substitution with units, answer with units) W= m*10.0m/s2 W= 70kg *10.0m/s2 W= 700 N

  29. What is the force of gravity on a 3.1 kg dog? W=mg W= 3.1 * 10.0 m/s2 W= 31.0 N

  30. Velocity vs Acceleration • When we talk about Newton’s laws, we will talk a lot about velocity and acceleration. • Velocity is how an object changes position from one point to another. • It is how fast or slow the object changes position and in which direction it travels. • Acceleration measures how fast or how slow an object speeds up or slows down. • How fast or how slow it takes an object to reach its traveling speed.

  31. Citations • Images from Google • Physical Science text • Images and information from http://www.space.com/15898-isaac-newton.html

More Related