March 4, 2016 What is acceleration?

Chapter 10: Motion Physical Science Coach Mynhier

Lesson 1: Measuring Motion Objectives Explain the relationship between motion and a frame of reference Relate speed to distance and time Distinguish between speed and velocity Solve problems related to time, distance, displacement, speed, and velocity.

Motion: an objects change in position relative to a reference point. Reference point: a stationary object You can tell if something is in motion by looking at the reference points around it. Looking out the window of a car Out on a cruise ship, out of a plane window

To accurately describe motion you need to know how far an object moves. Displacement: the change in position of the object. Your House Friend’s House School (A) (B) (C) A student walks from his house to a friend’s house (A), and then from his friend’s house to school (B). Line (A) plus line (B) equals the total distance he traveled. Line (C) is the total displacement.

There are two differences distance and displacement: Straightness and direction. Distance can be a straight line, but doesn’t have to be. Displacement must be a straight line. Also, displacement must be in a particular direction. The distance between school and your house may be 12 blocks. That doesn’t tell you which direction. Must be 12 blocks toward school.

Speed and Velocity Speed describes how fast an object moves. To measure speed you must measure two quantities: The distance traveled and the time it took to travel that distance (mph). The SI unit for speed is meters/second (m/s). When an object covers equal distance in equal amounts of time it is moving at constant speed. If a racecar has a constant speed of 96 m/s, it is traveling 96 meters every second.

Average Speed Most objects do not move at a constant speed. Speed of an object can change from moment to another. Average speed is equal to the distance traveled divided by the time needed to travel that far. Speed= distance= d time t

Velocity Describes speed and direction. In 1997 a lion escaped from a zoo in Florida. The lion was located by searchers in a helicopter because the velocity was reported. The lion’s escape speed could have been reported as 4.5 m/s. But which direction? It had to be reported as 4.5 m/s north, or toward the highway. Velocity must have direction.

THE MATH!! Suppose a soap box derby racer finishes a 132 m race in 18 s. By inserting the time and distance measurements into the formula, you can calculate average speed. V= d/t V= 132 m 18 s. V= 7.3 m/s v D t

Lesson 2: Acceleration Acceleration: the rate at which velocity changes over time. An object accelerates if its speed, direction, or both change. Acceleration can be a change in speed. If you speed up 1 meter per second, every second, you are accelerating.

Acceleration can also be a change in direction. Remember, velocity is defined as speed and direction. So if acceleration is a change in velocity, a change in your direction would be considered acceleration. You can accelerate without ever speeding up or slowing down if you are only changing direction.

Calculating Acceleration Acceleration Equation (for straight-line motion) Acceleration= final velocity –initial velocity time Or v 2 -v 1 Or a= Δv t t

Lesson 3: Force and Motion What is force? “The storm had a lot of force!” “Our team is a force to be dealt with!” “May the force be with you.” Force is defined as anything that changes the state of rest or motion of an object. Lesson 3: Force and Motion

The Force of Friction Friction: a force that opposes motion between two surfaces that are in contact. Friction opposes the applied force Because of friction, a constant force must be applied to keep it moving. The engine of a car must keep running in order to keep the a car rolling.

Static Friction is greater than kinetic friction Static Friction: friction between static surfaces. Kinetic Friction: friction that opposes movement of two surfaces that are in contact and sliding over one another. The force required to make a stationary start moving is usually greater than the force necessary to keep it moving.

Air Resistance Also Opposes Motion Any object moving through a fluid encounters friction between the surface of the object and the fluid. Car through the air, swimming through water.

Harmful Friction can be Reduced Two ways: liquid lubrication and gaseous lubrication Friction in an engine can cause extreme heat. What do we use in the engine? Can you give an example of a gaseous lubrication to reduce friction?

Reducing Harmful Friction (cont.) Make surfaces smoother. Competitive swimmers or bikers wear skin tight clothing to make themselves more streamlined.

Helpful Friction can be Increased Sand scattered on icy roads in the winter. Football players wear gloves to catch footballs. Pushing harder while scrubbing dishes.

Study Guide Page 323#’s 1-3 Page 324#’s 2, 3, 5 Page 328#’s 1-5 Page 330#’s 3 & 4 Page 338#’s 1, 2, 4-7, Write Complete sentences Show all of your Work`