Science Starter Take out last nights homework We

Science Starter • Take out last night’s homework • We are going to go over it together

Problem 1 • John drove South 120 km at 60 km/h and then East 150 km at 50 km/h. a) Draw and label the vectors • b) Determine the average speed for the whole journey?

Problem 2 • If I can walk at an average speed of 5 km/h, how many miles I can walk in two hours?

Problem 3 A man walked from point A to F following the route in the grid below in 3250 seconds. Determine a) the average speed, in m/s, for the whole journey. b) the magnitude of the displacement. c) the magnitude of the average velocity, in m/s, for the whole journey.

Problem 4 • A runner makes one lap around a 200 m track in a time of 25. 0 s. What was the runner's average speed?

Problem 5 • Light and radio waves travel through a vacuum in a straight line at a speed of very nearly 3. 00 108 m/s. How far is light year (the distance light travels in a year)?

Problem 6 • A motorist travels 406 km during a 7. 0 hr period. What was the average speed in km/hr and m/s?

Problem 7 • A bullet is shot from a rifle with a speed of 720 m/s. What time is required for the bullet to strike a target 3240 m away?

Agenda • Science Starter • Intro to Acceleration • Lab

Objective • SWBAT define and calculate acceleration

Change in Velocity • Each time you take a step you are changing the velocity of your body. • You are probably most familiar with the velocity changes of a moving bus or car. • The rate at which velocity (speed or direction) changes occur is called acceleration.

Vocab • Acceleration - The acceleration of an object is a measure of how quickly its velocity changes.

Formulas Acceleration= final velocity- starting velocity time Change in velocity = final – velocity Acceleration= change in velocity time starting velocity

Positive acceleration Negative acceleration

What is acceleration? A train accelerates in a straight line from rest. As it does, its velocity increases. The brakes on this motorcycle are causing it to slow down. This is negative acceleration or deceleration.

How is acceleration calculated? The acceleration of an object can be calculated using this equation: acceleration = change in speed time taken l Change in speed is measured in metres per second (m/s). l Time taken is measured in seconds (s). l Acceleration is measured in metres per second (m/s 2).

Acceleration problem A racing car accelerates from rest to a speed of 60 m/s in a time of 4 seconds. What is the acceleration of the car? acceleration = = change in speed 60 time taken 4 = 15 m/s 2

Using a formula triangle A formula triangle helps you to rearrange a formula. The formula triangle for acceleration (a), speed (s) and time (t) is shown below. So to find acceleration (a), cover up a… x …which gives the formula… a = s t Cover the quantity that you are trying to work out.

Acceleration problem A hungry cheetah spots a gazelle and decides to chase it. The cheetah accelerates at 10 m/s 2 from rest until it reaches 20 m/s. How long did this take? change in speed acceleration = time taken = 20 10 = 2 s = time taken change in speed acceleration

- A constant acceleration produces a straight line or linear slope (rise/run). - The slope of a nonlinear velocity-time graph (rise/run) will predict an objects instantaneous acceleration. a = v/t

A car traveling at 60 mph accelerates to 90 mph in 3 seconds. What is the car’s acceleration? Acceleration = Velocity(final) - Velocity(original) time = = 90 mph - 60 mph 3 seconds 30 mph 3 seconds = 10 mph/second

A car traveling at 60 mph slams on the breaks to avoid hitting a deer. The car comes to a safe stop 6 seconds after applying the breaks. What is the car’s acceleration? Acceleration = Velocity(final) - Velocity(original) time = = 0 mph - 60 mph 6 seconds = - 10 miles per hour per second