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Ocean Drifters – Investigating Ocean Currents
Activity 2: The Race is On  Teacher
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A. Speed:
Speed is a measure of how fast an object (including people) moves
across a given distance. To calculate speed we take the distance covered
and divide by the time it took to cross that distance:
Speed (m/s) = Distance (m) / Time (s)
Many different units can be used to describe speed. For instance,
if you are calculating the speed of a train, you may want to use
mph (miles per hour) or kph (kilometers per hour). However, if you
are tracking the path of a snail, you may want to use cm/h (centimeters
per hour) or in/h (inches per hour).
Practice calculating speed using different units for the examples
given below.
Object

Distance

Time

Speed

Airplane

700 miles

2 hours

350 mph

Snail

1.2 cm

1.5 hours

0.8 cm/h
(.0005 mph)

Whale

25 nm*

5 hours

5 nmph (knots)

Cheetah

24 miles
(38 km)

15 minutes
(.25 hours)

96 mph

* nautical miles
When making charts to show currents, scientists often use arrows
to represent speed. The size of the arrow is proportional to the
speed. If 1 cm = 1 mph, then the airplane’s speed could be
represented by an arrow that is 350 cm long. Yikes! That is a long
arrow! In this case it would be better to use 1 cm = 35 mph. Then
our arrow would be only 10 cm long.
If we use 1 cm = 1mph, then the snail’s arrow would only be
0.8 cm long. That arrow is a short arrow. Using 1 cm = 10 mph, draw
below the arrows which would represent the speeds of the whale and
cheetah.
B. Direction of movement:
Speed
describes how fast or slow an object moves, but it does not tell
us anything about the direction of movement. If we combine the speed
and direction of an object, it is called velocity. Velocity can
be shown using a vector (an arrow which shows direction and speed).
On maps and charts there is usually a compass rose. The compass
rose shows northsoutheastwest directions on a map. To the right
is an example.
N = North, S = South, W = West, E = East
If a direction is between 2 of the major directions (N,S, E and
W), then the directions are combined. An arrow pointing to a direction
between North and East, would be pointing Northeast (NE). What direction
do these arrows point?
For each of the arrows below, measure its length. Using a scale
of 1 cm = 10 mph, determine what speed it represents and name the
direction it is pointing (this is its velocity).
Draw arrows which represent the speed and direction for the following
velocities.


a. South (20 mph)

b. Southwest (30 mph) 
This activity was adapted from "Track a NOPP Drifter" written by
Anna C. Switzer for the NOPPConsortium of Oceanographic Activities
for Students and Teachers (COAST). To find out more, please visit
Project NOPP Drifters and
Consortium for Oceanographic
Activities for Students and Teachers. All rights reserved.
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