Embedded Files
by Year 9 students
This page contains Physics contents discussed in class and re-written by students in prose form to show how well they understood the materials with some elements of creativity and link to the holistic being that the school is promoting through the P.I.A.G.E.T. values. Classmates read the contributions when doing home revisions and/or serve as peer support to others may have fall short of the standard, failed to earned the content-based badges.
Contributions in this page are also part of the 5% PROJECT component of the Final Grade in each term of the school year.
Non-uniform Acceleration and Terminal Velocity
Explained by Alvin, 2 September 2020
An object falling reaches terminal velocity
Firstly, we need to understand the term freefall. Freefall, on Earth, is at 9.81 m/s2, but let’s regard that as 10 m/s2. Now, terminal velocity is when the drag force (acceleration) is equal to the downward force (gravity).
As the speed of an object increases, so does its drag force. At a certain point, when both forces are equal, the object stops accelerating, and starts moving at constant speed, or otherwise terminal velocity. If an object moves at a speed faster than terminal velocity, it will slow down until it reaches terminal velocity.
The object’s drag [Fd] depends on its projected area, or the cross-section of the object on a horizontal plane (two-dimensional). For instance, a parachute (large projected area relative to its mass) will have a lower terminal velocity as compared to a bullet (small projected area relative to its mass).
Non-uniform acceleration
As we know, gravitational acceleration is at 9.81 m/s2, or regarded as 10 m/s2. But when we have another force, drag force, acceleration will decrease over time and reach Terminal velocity. Remember, as an object’s speed increases, so does its drag force.
Let’s take an example:
A man who weighs 70 kg is going skydiving. At 0 seconds, there is no drag force and his acceleration is equal to gravity acceleration.
But as he falls, the drag force (air resistance) starts to act on him. At 4 seconds, we cay say that the drag force acting on him makes the acceleration less than the acceleration due to gravity.
At 8 seconds, the drag force acting on him is 700N, otherwise equal to his weight, and he stops accelerating. Meaning that the fall is not acceleration anymore but a constant speed downward which is known as Terminal velocity.
The figure at the right is an acceleration-time graph showing the man’s fall.
Speed, Velocity and Acceleration
Described by Cayla, 2 September 2020
The differences between speed and/from velocity.
Speed, being a scalar quantity, is the rate at which an object covers distance, while velocity is the rate at which the position changes and is also a vector quantity.
How is acceleration related to speed and velocity?
We learned that speed is a scalar quantity, which is one that requires only a magnitude, while velocity is a vector quantity, requires a magnitude and a direction. The rate of change for velocity is acceleration, which is measured in displacement over time over time (e.g. m / s^2).
Recall and use average speed = distance travelled / time taken
This is when:
distance travelled is measured in metres (m)
average speed is measured in metres per second (m/s)
time is measured in seconds (s)
A car travels 750 m in 98 s, then 800 m in 60 s. Calculate its average speed for the whole journey.
First calculate the total distance travelled:
750 + 800 = 1550m
Then calculate the total time taken:
98 + 60 = 158s
Use the formula to calculate average speed:
Average speed = distance travelled/time taken
1550/158 = 9.81 m/s
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