Forces! - The most attractive thing in physics
A force is any influence that causes an object to undergo a specific change. This can be a force such as gravity which attracts objects or thrust, which increases the velocity of an object.
Issac Newton, after he discovered gravity, stated that gravity was a force that acts between two masses. The larger the mass, the larger the gravitational force between them. This is why you don't see pens attracting boulders but don't float off since you are being held down by gravity.
Another force that is pretty common in everyday life is friction. When two surfaces slide past each other, it creates a force of friction which is a force that opposes the motion. For instance, if you had a wooden block and you slid it across a table then there would be some resistance which would be friction that is counteracting the force of the motion aka. you moving the block. Another example would be walking, your foot creates friction against the floor which creates a backward force that the floor has to counter by pushing against your foot. As a result, the floor stays still while you move forward.
An object can have many forces acting on it at any one time but they can all be added to give a resultant force. If the resultant force is zero, a moving object will stay at the same speed. this outcome in a resultant force is said to be in equilibrium. Equilibrium is a word used in a lot of different sciences and is best described as a state when opposite influence, or in this case forces, are balanced.
However, if this resultant force is not in a state of equilibrium it will cause the moving object so slow down or speed up depending on which force is smaller. If the object speeds up this means that the resultant force is in the same direction as the object is moving and therefore means less friction so the moving force accelerates the object. If an object is slowing down the resultant force is in the opposite direction of the motion so the friction is greater, this type of physics is used to create parachutes.
To calculate the force of an object you need two things the acceleration and mass.
- The resulting force is measured in Newtons, N
- The mass is measured in kilograms, kg
- The acceleration is measured in meters per second squared, m/s2
And the equation looks like this;
Force = mass x acceleration or F = kg x m/s2
A huge mistake newcomers to physics make it that they think mass is the same as weight, THEY ARE NOT!!
The mass of an object is how much matter, or 'stuff', there is in an object. Whereas weight is a force acting on that matter. In physics weight usually, realtes to a term given when gravity is acting on mass.
A good way to remember the difference when it comes to equations is weight is measured in Newtons because newtons discovery of gravity is acting on it. Mass is how massive something is so it wants to be told the amount of matter there is in it so it wants kilograms, not newtons.
To calculate the weight of a moving object the equation is;
Weight (N) = mass (kg) x gravitational field strength(N/kg)
The gravitational field strength of earth is about 9.8N/kg. This means that the weight of an object on earth is different to that on the moon because there is less gravitational field strength.