Forces and Newton’s Laws
Let’s hear it for the man himself, Mr Calculus, Mr Gravity, Mr Motion:
Make way for ISAAC NEWTON everybody!
In this section we will discuss and apply the basics of this rockstar’s workings and break down his famous three laws of motion.
Newton’s First Law and Unbalanced forces
Newton’s first law states that if a body is at rest or moving at a constant velocity in a straight line, it will remain at rest or at a constant velocity in a straight line unless an unbalanced force is acted upon it.
So what does this mean? If I stood still, I will remain still standing unless someone pushed me. Likewise, a car driving on the motor-way at the same speed will continue to do so unless it presses the breaks, or presses the accelerator.
Newton’s Second Law
Newton’s second law can be summarised by the following equation.
Force = mass x acceleration
F = ma
Where F is Force in Newtons (N)
m is mass in kilograms (kg)
a is acceleration in (ms^-2)
Newton’s Third Law
This one is very poetic and often reeled off in multiple movies and TV shows -
“Every action has an equal and opposite reaction.”
A rocket is launched into space and gains thrust by the opposite force that the jet engine fuel pushes against the Earth.
Weight
Weight and Mass are different entities. Weight is the force that an object has towards the ground, and it is dictated using mass and gravitational field strength.
Gravitation field strength is the strength of the force of gravity on objects on a planet. The gravitational field strength is determined by the size of the planet, and Earth has a Gravitational field strength of 9.8Nkg^-1. Values of gravitational field strength on other planets can be found in the data booklet.
The weight equation is essentially the same as F=ma:
Weight = Mass x Gravitational Field Strength.
W = m x g
Free-fall and Terminal Velocity
Free fall is the motion of an object where gravity is the only force acting on it.
Terminal velocity occurs when a maximum velocity is reached, where the force of drag (air resistance) is balanced with the force of gravity. As these forces are balanced, there is no acceleration and so terminal velocity is reached.
Key Points!
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Newton's first law
If a body is at rest or moving at a constant velocity in a straight line, it will remain at rest or at a constant velocity in a straight line unless an unbalanced force is acted upon it.
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Newton's second law
Force = mass x acceleration
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Newton's third law
Every action has an equal and opposite reaction.
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Weight
Weight is the force that an object has towards the ground, and it is dictated using mass and gravitational field strength.
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Terminal Velocity
Free fall is the motion of an object where gravity is the only force acting on it.
Terminal velocity occurs when a maximum velocity is reached, where the force of drag (air resistance) is balanced with the force of gravity. As these forces are balanced, there is no acceleration and so terminal velocity is reached.