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? c) Determine the magnitude of the average velocity 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 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.

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 – starting

velocity velocity Acceleration= change in velocity

time

PositivePositive acceleration acceleration

Negative Negative accelerationacceleration

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.

What is acceleration?

The acceleration of an object can be calculated using this equation:

change in speed

time takenacceleration =

Acceleration is measured in metres per second per second (m/s2).

Change in speed is measured in metres per second (m/s).

Time taken is measured in seconds (s).

How is acceleration calculated?

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?

= 15 m/s2

change in speed

time takenacceleration =

= 60

4

Acceleration problem

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.

x

Cover the quantity that you are trying to work out.

So to find acceleration (a), cover up a…

…which gives the formula…

a =s

t

A hungry cheetah spots a gazelle and decides to chase it. The cheetah accelerates at 10

m/s2 from rest until it reaches 20 m/s. How long did this take?

acceleration = change in speedtime taken

= 2010

= 2 s

Acceleration problem

time taken = change in speedacceleration

- A constant acceleration

produces a straight line or linear slope

(rise/run).

- The slope of a non-linear velocity-time graph (rise/run) will predict an objects

instantaneous acceleration.

a = v/t

Acceleration =Velocity(final) - Velocity(original)

time

A car traveling at 60 mph accelerates to90 mph in 3 seconds. What is thecar’s acceleration?

=90 mph - 60 mph

3 seconds

=30 mph

3 seconds

= 10 mph/second

Acceleration =Velocity(final) - Velocity(original)

time

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 thecar’s acceleration?

=0 mph - 60 mph

6 seconds

=- 60 mph

6 seconds

= - 10 miles per hour per second