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Equations of Motion
AS Physics - Free Fall & Terminal Speed
Newton's 2nd Law:
Acceleration is needed to change velocity.
resultant force (N) = mass (kg) x acceleration (ms¯²)
Free Fall
F = m x a
Free fall is when there is only gravity and it is defined as the motion of an object undergoing an acceleration of 'g'.
- The more force you have acting on a certain mass, the more acceleration you get.
- For a given force the more mass you have, the less acceleration you get.
- Acceleration is a vector quantity - and 'g' acts vertically downwards.
- The magnitude of 'g' is usually taken as 9.81ms¯².
Equations of Motion
Newton's 1st Law:
- The only force acting on a free fall object is its weight.
All objects in free fall accelerate at the same rate
v = u + at
Newton's Laws of Motion
S = (v + u) t
2
- Objects can have an initial velocity in any direction and still undergo free fall as long as the force providing the initial velocity is no longer acting.
s = ut + ½at²
v² = u² + 2as
Force is needed to change velocity.
- Newton's first law of motion states that the velocity of an object will not change unless a resultant force acts on it.
- This means that a body will stay still or move in a straight line at a constant speed, unless there's a resultant force acting on it.
- If the forces aren't balanced, the overall resultant force will make the body accelerate. This could be a change in direction or speed or both.
Galileo believed that all objects fall at the same rate. The problem was that free-falling objects fell too quickly for him to be able to take any accurate measurements and prove his theory.
Newton's 3rd Law:
So Galileo measured the time a ball took to roll down a smooth groove in an inclined plane which was effective because by rolling it down a plane it slowed the ball's fall as well as reducing the effect of air resistance.
Each force has an equal, opposite reaction force.
I an object A exerts a force on object B, then object B exerts an equal but opposite force on object A.
By rolling the ball along different fractions of the total length of the slope, he found that the distance the ball travelled was proportional to the square of the time taken, the ball was accelerating at a constant rate.
- If you push against a wall, the wall will push back against you, just as hard and as soon as you stop pushing, so does the wall.
- If you pull a cart, whatever the force you exert on the rope, the rope exerts the exact opposite pull on you.