1 / 13

Chapter 6

Chapter 6. Application of Newton’s Laws. Outline. Frictional Forces Kinetic friction Static friction Strings and Tension Springs and Hooke’s Law for Spring Forces Various Examples. Frictional Forces.

brinly
Download Presentation

Chapter 6

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. Chapter 6 Application of Newton’s Laws Dr. Jie Zou PHY 1151 Department of Physics

  2. Outline • Frictional Forces • Kinetic friction • Static friction • Strings and Tension • Springs and Hooke’s Law for Spring Forces • Various Examples Dr. Jie Zou PHY 1151 Department of Physics

  3. Frictional Forces • The origin of friction: Even “smooth” surfaces have irregularities when viewed at the microscopic level. This type of roughness contributes to friction. • Two types of friction: • Kinetic friction • Static friction Dr. Jie Zou PHY 1151 Department of Physics

  4. Kinetic Friction • Kinetic friction fk: The friction encountered when surfaces slide against one another with a finiterelative speed. • Direction of the force of kinetic friction: Kinetic friction fk acts to oppose the sliding motion at the point of contact between the surfaces. • Magnitude of the force of kinetic friction: In general, the force of kinetic friction is found to be proportional to the magnitude of the normal force, N, or fk = kN. • The constant of proportionality, k, is referred to as the coefficient of kinetic friction. Dr. Jie Zou PHY 1151 Department of Physics

  5. Kinetic Friction: Example 6-1 • Someone at the other end of the table asks you to pass the salt. You slide the 50.0-g salt shaker in their direction, giving it an initial speed of 1.15 m/s. • (a) If the shaker comes to a rest with constant acceleration in 0.840 m, what is the coefficient of kinetic friction between the shaker and the table? Dr. Jie Zou PHY 1151 Department of Physics

  6. Kinetic Friction: Example 6-2 • A trained sea lion slides from rest with constant acceleration down a 3.0-m-long ramp into a pool of water. If the ramp is inclined at an angle of 23 above the horizontal and the coefficient of kinetic friction between the sea lion and the ramp is 0.26, how long does it take for the sea lion to make a splash in the pool? Dr. Jie Zou PHY 1151 Department of Physics

  7. Static Friction • Static friction fs: Static friction tends to keep two surfaces from moving relative to one another. • There is an upper limit to the force that can be exerted by static friction, fs,max. • fs,max = sN. The constant of proportionality is called s, the coefficient of static friction. • Magnitude: The force of static friction, fs, can have any value between zero and fs,max. • Direction: The direction of fs is parallel to the surface of contact, and opposite to the direction the object would move if there were no friction. Dr. Jie Zou PHY 1151 Department of Physics

  8. Static Friction (Cont.) Dr. Jie Zou PHY 1151 Department of Physics

  9. Static Friction: Example 6-3 • A flatbed truck slowly tilts its bed upward to dispose of a 95.0-kg crate. For small angles of tilt the crate stays put, but when the tilt angle exceeds 23.3 the crate begins to slide. • (a) What is the coefficient of static friction between the bed of the truck and the crate? • (b) Find the magnitude of the static friction acting on the crate. Dr. Jie Zou PHY 1151 Department of Physics

  10. Strings and Tension: Example 6-5 • To hang a 6.20 kg pot of flowers, a gardener uses two wires-one attached horizontally to a wall, the other sloping at an angle of  = 40.0 and attached to the ceiling. Find the tension in each wire. Dr. Jie Zou PHY 1151 Department of Physics

  11. Springs and Hooke’s Law • Springs and Hooke’s Law • Magnitude of the spring force: The spring force is proportional to the amount, x, by which it is stretched or compressed. • Direction of the spring force: the force is opposite to the displacement, that is the it is restoring. • Hooke’s Law: F = - k x. • k: Force constant of the spring, units: N/m. Dr. Jie Zou PHY 1151 Department of Physics

  12. Springs and Hooke’s Law: Exercise 6-1 • A 1.50-kg object hangs motionless from a spring with a force constant k = 250 N/m. How far is the spring stretched from its equilibrium length? Dr. Jie Zou PHY 1151 Department of Physics

  13. Homework • Chapter 6, Page 165, Problems: #1, 7, 9, 19. Dr. Jie Zou PHY 1151 Department of Physics

More Related