What is a pulse, Grade 10 Physics
1/What is a pulse

Activity :: Investigation : Observation of Pulses
Take a heavy rope. Have two people hold the rope stretched out horizontally.
Flick the rope at one end only once.

What happens to the disturbance that you created in the rope? Does it stay at the place where it was created or does it move down the length of the rope?
In the activity, we created a pulse. A pulse is a single disturbance that moves through a medium. A transverse pulse moves perpendicular to the medium. Figure 5.1 shows an example of a transverse pulse. In the activity, the rope or spring was held horizontally and the pulse moved the rope up and down. This was an example of a transverse pulse.

Definition: Pulse
A pulse is a single disturbance that moves through a medium.

2/ Pulse Length and Amplitude
The amplitude of a pulse is a measurement of how far the medium is displaced from a position of rest. The pulse length is a measurement of how long the pulse is. Both these quantities are shown in Figure 5.1.

Activity :: Investigation : Pulse Length and Amplitude
The graphs below show the positions of a pulse at different times.

Use your ruler to measure the lengths of a and p. Fill your answers in the table.

What do you notice about the values of a and p?
In the activity, we found that the values for how high the pulse (a) is and how wide the pulse (p) is the same at different times. Pulse length and amplitude are two important quantities of a pulse.

3/ Pulse Speed

Definition: Pulse Speed
Pulse speed is the distance a pulse travels in a specific time.

In Chapter 3 we saw that speed was defined as the distance travelled in a specified time. We can use the same definition of speed to calculate how fast a pulse travels. If the pulse travels a distance d in a time t, then the pulse speed v is:

\[v = \dfrac{d}{t}\]​

Worked Example 1: Pulse Speed
Question: A pulse covers a distance of 2 m in 4 s on a heavy rope. Calculate the pulse speed.
Answer
Step 1 : Determine what is given and what is required
We are given:

• the distance travelled by the pulse: d = 2 m
• the time taken to travel 2 m: t = 4 s

We are required to calculate the speed of the pulse.
Step 2 : Determine how to approach the problem

We can use: \[v = \dfrac{d}{t}\]​

to calculate the speed of the pulse.
Step 3 : Calculate the pulse speed

v = d/t = 2 m/ 4 s = 0,5 m · s$^{−1}$​

Step 4 : Write the final answer
The pulse speed is 0,5 m·s$^{−1}$

Important: The pulse speed depends on the properties of the medium and not on the
amplitude or pulse length of the pulse.

Exercise: Pulse Speed
E - 1. A pulse covers a distance of 5 m in 15 seconds. Calculate the speed of the pulse.

E - 2. A pulse has a speed of 5 cm.s$^{−1}$. How far does it travel in 2,5 seconds?

E - 3. A pulse has a speed of 0,5 m·s$^{−1}$. How long does it take to cover a distance of 25 cm?

E - 4. How long will it take a pulse moving at 0,25 m·s$^{−1}$ to travel a distance of 20 m?

E - 5. Examine the two pulses below and state which has the higher speed. Explain your answer.


E - 6. Ocean waves do not bring more water onto the shore until the beach is completely submerged. Explain why this is so.

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Physics 10.IV Transverse Pulses

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