Motion: Speed, Velocity, and Acceleration

Flashcards covering key definitions, formulas, and concepts of motion including speed, velocity, acceleration, and free fall based on the IGCSE Physics curriculum.

What is the definition of speed?

Speed is the distance travelled per unit time.

What is the formula for average speed?

$$\text{Average speed} = \frac{\text{total distance travelled}}{\text{total time taken}}$$

What is the definition of velocity?

Velocity is speed in a given direction.

What is the formula for velocity?

$$\text{Velocity} = \frac{\text{displacement}}{\text{time taken}}$$

What is the difference between distance and displacement in Figure 2.4 where a car travels $5\,km$ due east and then $7\,km$ back?

The distance covered is $12\,km$ ($5\,km + 7\,km$), while the displacement is $-2\,km$ (or $2\,km$ due West).

Define acceleration.

Acceleration is the change of velocity per unit time.

What is the formula for acceleration? Provide the meaning of each variable.

$a = \frac{v - u}{t}$ where $v = \text{final velocity}$, $u = \text{initial velocity}$, and $t = \text{total time taken}$. ($\Delta v / \Delta t$)

What is the standard unit for acceleration?

Metre per second per second ($m/s^2$).

What does the gradient of a distance-time graph represent?

The speed of the object.

Describe the speed of an object when the gradient of its distance-time graph is zero.

The object is at rest or stopping, and its speed is $0\,m/s$.

What does a decreasing gradient on a distance-time graph indicate about an object's motion?

The speed is decreasing, meaning the object travels slower each second.

What does the gradient of a speed-time graph represent?

The acceleration of the object.

How is the distance travelled determined from a speed-time graph?

By calculating the area under the speed-time graph.

What is the approximate value of the acceleration of free fall $g$ for an object near the surface of the Earth?

$9.8\,m/s^2$.

In the 17th century, what did Galileo Galilei discover regarding falling objects?

He discovered that all objects fell at the same acceleration due to the Earth’s gravity, regardless of mass or size.

What is meant by an object in "free fall"?

An object in free fall is one where only its own weight acts on it, moving with constant acceleration (if air resistance is negligible).

What are the characteristics of air resistance?

It is a frictional force that opposes motion, increases with the surface area (or size) of objects, increases with the density of air, and increases with the speed of moving objects.

Under what condition does a falling object achieve terminal velocity?

When the weight of the object equals the air resistance.

Describe the motion of a falling sponge between its release and reaching terminal velocity.

Initially, its speed increases uniformly at a rate of $9.8\,m/s^2$. Then, its speed continues to increase but at a decreasing rate (decreasing acceleration) until it reaches terminal velocity with zero acceleration.

If a toy car travels $96\,m$ in $12\,s$, what is its average speed?

$8\,m/s$.

Calculate the acceleration of a golf ball if its velocity changes from $8\,m/s$ to $14\,m/s$ in $10\,s$.

$0.6\,m/s^2$.