Understanding Free-Fall (acceleration due to gravity)

On earth, the gravitational field strength is 10 N/kg and the acceleration due to gravity is 10 ms-2.

That means when you release an object from you hand, the object will fall with increasing speed. The acceleration is a constant 10 ms-2 (acceleration due to gravity). Simply put, it means in 1 second, the speed of the object will increase by 10 m/s.

In general, if there is no air resistance or air resistance is negligible, the speed-time graph is a straight line with constant gradient and passes through origin, i.e. speed is directly proportional to the time.

If there is air resistance, there is a maximum constant speed if the object continues to fall. Hence the graph is different.

More importantly, remember that any object that you released on earth, whether there is air resistance or no air resistance, the initial acceleration when it is released is always a constant 10 ms-2!

Refer to the video for the explanation and some examples.

Different Types of Vector Diagrams

Vector diagram is commonly referred to parallelogram diagram.

Vector diagrams are generally divded into 3 categories:

1) 2 forces acting on a body, there is a resultant force. (Newton’s 2nd Law)

2) 3 forces acting on a body, the body is at rest / in equilibrium or moving at constant speed. (Newton’s 1st Law, Net force = 0N) 

– The resultant force due to any 2 forces is equal and opposite to the 3rd unknown force.

3) 3 forces acting on a body, the body is at rest / in equilibrium or moving at constant speed (Newton’s 1st Law, Net force = 0N)   

– Only 1 known force, angles given, using closed loop triangle to find the 2 unknown forces.

Let’s look at some examples for each category.

1) 2 forces acting on a body, there is a resultant force. (Newton’s 2nd Law)

2) 3 forces acting on a body, the body is at rest / in equilibrium or moving at constant speed. (Newton’s 1st Law, Net force = 0N)

– The resultant force due to any 2 forces is equal and opposite to the 3rd unknown force.

– You can either use parallelogram rule or closed looped triangle.

Example 1: Body at rest – Using Parallelogram Rule

Example 1: Body at rest – Using Closed-Looped Triangle

Example 2: Body at constant speed – Using Parallelogram Rule

Example 2: Body at constant speed – Using Closed-Looped Triangle

3) 3 forces acting on a body, the body is at rest / in equilibrium or moving at constant speed (Newton’s 1st Law, Net force = 0N)

    – Only 1 known force, angles given, using closed loop triangle to find the 2 unknown forces.

Example 1

Example 2

Oscillating or Vibrating Object in a Wave Motion

When an object is oscillating or vibrating in a wave motion, the speed of the object varies along the path.

In this video, there are 3 examples of vibrating object.

1) Mass vibrating vertically from a spring

2) Pendulum bob oscillating

3) A particle vibrating up and down on a transverse wave

In general, when the object is at the extreme ends of the oscillation or vibration, it is momentarily at rest. Hence its KE at these points is minimum or 0 J.

And in the middle that is where the object is travelling the fastest, hence the KE is the maximum.