A free falling object is an object that is falling under the sole influence of gravity. Any object that is being acted upon only by the force of gravity is said to be in a state of free fall. There are two important motion characteristics that are true of free-falling objects:
- Free-falling objects do not encounter air resistance.
- It accelerates downwards at a rate of 9.8 m/s2.
Because free-falling objects are accelerating downwards at a rate of 9.8 m/s2, a dot diagram of its motion would depict acceleration. The dot diagram at the right depicts the acceleration of a free-falling object. The position of the object at regular time intervals – say, 0.1 second is shown. The fact that the distance that the object travels every interval of time is increasing is a sure sign that the ball is speeding up as it falls downward. An object travels downward and speeds up, and then its acceleration is downward.
Uniform Gravitational Field without Air Resistance
Where:
v0 – is the initial velocity (m/s)
v0 – is the initial velocity (m/s)
v(t) – vertical velocity with respect to time (m/s)
y0 – initial altitude (m)
y(t) – altitude with respect to time (m)
t – time elapsed
g – acceleration due to gravity
Problem ~
An object in free fall is said to have reached terminal velocity. If the air resistance becomes strong enough to counter act all gravitational acceleration, causing the object to fall at a constant speed. The exact value of the terminal velocity varies according to the shape of the object, but can be estimated for many objects at 100m/s. When a 10kg object has reached terminal velocity, how much power does the air resistance exert on the object?
Solution:
To solve this problem, we will use the equation P = Fv cos θ instead of the usual power equation, as we are given the velocity of the object. We merely need to calculate the force exerted on the object by the air resistance, and the angle between the force and the velocity of the object. Since the object has reached a constant speed, the net force on it must be zero. Since there are only two forces acting on the object, gravity and air resistance, the air resistance must be equal in magnitude and opposite in direction as the force of gravity. Thus, Fa = - F6 = mg 98N , pointing upwards. Thus, the force applied by air resistance is anti-parallel to the velocity of the object. Thus:
To solve this problem, we will use the equation P = Fv cos θ instead of the usual power equation, as we are given the velocity of the object. We merely need to calculate the force exerted on the object by the air resistance, and the angle between the force and the velocity of the object. Since the object has reached a constant speed, the net force on it must be zero. Since there are only two forces acting on the object, gravity and air resistance, the air resistance must be equal in magnitude and opposite in direction as the force of gravity. Thus, Fa = - F6 = mg 98N , pointing upwards. Thus, the force applied by air resistance is anti-parallel to the velocity of the object. Thus:
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