GSCE Physics - Physics - P6

Topics

• Scalar and Vector
• Contact and Non-Contact Forces
• Gravity
• Resultant Force
• Force and Elasticity 

Scalar and Vector

• Scalar - Magnitude but no Direction
• Vector - Magnitude and Direction 

Vectors can be represented with an arrow representing the magnitude or size of the force. Examples of scalar include power, mass, time, speed, distance, energy and temperature. Examples of vectors include velocity, acceleration, force, displacement and weight. 

Contact and Non-Contact Forces

A force is a vector quantity since it is measured with a magnitude/size and a direction. The force size is shown by the extent of the arrow and the arrow also indicates its direction.

• Contact Force - interaction equals results

An example of a contact force is friction as two surfaces have to interact and come into contact with it to occur. Other examples are air resistance. tension and normal contact force.

• Non-Contact Force - physically separate equals results  

An example of a non-contact force is gravity as it acts through the air to occur. Other examples are magnetic force and electrostatic force.

Gravity

• Weight - force acting downwards, measured in Newtons, N
• Mass - volume, measured in Kilograms, kg

Even though, mass and weight are different values they are directly proportional and can be converted through the equation: Weight = Mass x Gravitational Force. Gravitational force is measured in Newtons per kilograms and changes because of the strength of gravity on a planet. So, in space, you are weightless as you have weight but your mass remains the same. This is because the chemical composition and atomical structure of your body has not changed at all, only your location. 

Weight can be measured with a Newton meter. Weight is considered to act on a single point but weight is across your entire body. Therefore, a scale shows your force downwards. 

Resultant Force

Resultant Force is the result of force acting opposite each other. For example, if a plane has a thrust force of 10N and a drag or air resistance force of 4N, the resultant force would be 6N, because it is the difference between the two. The resultant force acts in the direction which was the strongest.

47N<●>23N

In this example the resultant force would be backwards, with a force of 24N. You use diagrams like this to represent the forces occuring or acting on an object.

13N <●>13N

However, in this example the forces are equal. Even though this is the fact, you still take them away from each other and get the resultant force of 0N, which acts in either direction as the object doesn't move.

Resultant Force

In some cases you will be asked to work out the missing force on a diagram. There are two different examples of this question, working out the palleogram of forces and the triangle of forces.

In the palleogram of forces you will be given two forces acting in a direction. The measurement of Newtons will be per cm. So if you had a force of 300N acting across 3cm, you would know that, 100N acts across 1cm.

In a triangle of forces you will be given however number of forces in different directions and be asked to calculate a missing force. You will need to move the arrows, using the same position to form a right angled triangle. Using Phyathogras therom, you can then work out the missing force.

Forces and Elasticity

Forces act all around us. They are either push, pull of twist and act upon contact or happen if there is no object.

When you are trying to change the shape of an object, there are several forces acting on the object as you compress it and try and change its shape. The object has tension which keeps its shape. Gravity and compressing forces acts downwards onto it as you compress it. The process of this is called deformation and the elasticity of an object will tell if it returns to its original shape.

Forces and Elasticity

Force is equal to extension and you can work this out using the equation Force = Spring Constant x Extension.The amount an object is streched is directly propotional to the force applied, and this Hooke's Law.

Hooke's Law is 'the extension of a spring is directly proportional to the force applied, provided its limit of proportionality is not exceeded' or extension = force

Work applied to an object changes its shape and therefore the object then has elastic potential energy to return to its original shape. This energy can be calculated using the equation Stored Elastic Potential Energy = 1/2 Spring Constant × Extension^2. The more you strech an object the more force is applied so there is more elastic potential energy stored in the object. 

On a graph you can show the features of a spring. 

• Straight Line which is constant and diagonal- Elastic Region
• Before Curve - Limit of Proportionality/Elastic Limit
• Curve - Plastic Region
• Straight Line - Break Point

Plastic - cannot return to original. Elastic - can return to original. Both apply after extension.

Work Done and Energy Transfers

Work done is the measurement of energy showing how a force acting on an object will turn out. You can use this equation to work it out, Work Done/Energy = Force × Distance.

One unit of energy, a joule is equal to one unit of force, a Newton.

Friction causes heat when it is used in a reaction, because two forces interact. The extremity is down to the speed of the object and the surface in question.