Textbook 🔗
- Collect a sciPad
- Name it
- Bring it to class (and home) every day in case of illness
Ngā Whāinga Ako 🔗
- Name the metric units of distance, time and speed and give their symbols.
- Define the term speed.
- Calculate the average speed of objects. Use $v=d/t$.
What is Speed? 🔗
Head up “Speed” in your book"
You know that someone who finishes a race in the shortest time is the fastest. That they have the highest speed.
Speed is the amount of distance covered in some amount of time.
Units of Speed 🔗
- Cars display their speed in kilometers per hour
- In Physics we prefer to give speed in the number of meters travelled in one second.
- We call this meters per second.
Calculating Speed 🔗
To calculate speed we need to know two things!
- Distance: has unit meters (m) and is represented by symbol $d$ in equations.
- Time: has unit seconds (s) and is represented by symbol $t$ in equations.
Speed vs Velocity 🔗
- Speed is a measure of distance covered in a certain amount of time.
- e.g 13 meters per second
- Velocity includes a direction
- e.g. 13 meters per second east
How to Calculate Velocity 🔗
$$
\begin{aligned}
velocity &= \frac{\text{change in distance}}{\text{change in time}} \newline
v &= \frac{\Delta d}{\Delta t} \newline
\end{aligned}
$$
It is measured in meters per second, also shown as $\frac{m}{s}$ or $ms^{-1}$.
How Do We Solve Problems? 🔗
- Knowns
- Unknowns
- Formula
- Substitute
- Solve
Question 1: Velocity 🔗
A rock climber climbs 15 meters in 5.48 seconds. What velocity was he travelling?
Question 1: Answer 🔗
- Knowns: $\text{distance (d)}=15m$, $\text{time (t)} = 5.48s$
- Unknowns: $\text{velocity (v)}$
- Formula: $v = \frac{\Delta d}{\Delta t}$
- Substitute: $v = \frac{15}{5.48}$
- Solve: $v = 2.74\frac{m}{s}$
Question 2 🔗
- Mr Le Sueur ran 4.61km in 21 minutes and 16 seconds. How fast did he run?
- Hint: Convert the time and distance to Standard International Units
Question 2: Answer 🔗
- Knowns: $\text{distance (d)} = 4.61km = 4610m$, $\text{time (t)} = 21min, 16s = 1276s$
- Unknowns: $\text{velocity (v)}$
- Formula: $v = \frac{\Delta d}{\Delta t}$
- Substitute: $v = \frac{4610}{1276}$
- Solve: $v = 3.61\frac{m}{s}$
Question 3 🔗
- Mr Le Sueur ran at $1.51\frac{m}{s}$ for 1hr, 18min and 11 seconds. How far did he run?
- Hint: Convert the time to Standard International Units
Question 3: Answer 🔗
- Knowns: $\text{velocity (v)} = 1.51\frac{m}{s}$, $\text{time (t)} = 1hr, 18min, 11s = 4691s$
- Unknowns: $\text{distance (d)}$
- Formula: $v = \frac{\Delta d}{\Delta t}$
- Substitute: $1.51 = \frac{d}{4691}$
- Solve: $1.51 \times 4691 = d = 7083.41m$