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P5 - Forces

Scalar and Vector Quantities
1. Scalar quantities only have a magnitude or size.
2. Vector quantities have both magnitude and an associated direction.
3. The resultant force is a single force that has the same effect as two or more forces acting together.
Contact and non-contact forces
1. Contact forces are forces that act between two objects that are physically touching each other.
  1. An object at rest on a surface experiences reaction force. For example, a book on a table.
  2. An object that is being stretched experiences a tension force. For example, a cable holding a ceiling lamp.
  3. Two objects sliding past each other experience friction forces. For example, a box sliding down a slope.
  4. An object moving through the air experiences air resistance. For example, a skydiver falling through the air.
2. Non-contact forces are forces that act between two objects that are not physically touching each other.
  1. A magnetic force is experienced by any magnetic material in a magnetic field.
  2. An electrostatic force is experienced by any charged particle in an electric field.
  3. A gravitational force is experienced by any mass in a gravitational field.
Gravity
1. All objects with mass produce a gravitational field. The more mass an object has, the greater its gravitational field will be.
2. Weight is the force acting on an object due to gravity - it has the unit newtons (N) and acts towards the centre of a gravitational field.
3. The weight of an object can be measured using a calibrated spring-balance, often called a Newton meter.
4. weight = mass × gravitational field strength weight is newtons, mass is kilograms, gravitational field strength is newtons per kilogram (N/kg)
5. Work is done when energy is transferred from one store to another. Work is also done when a force causes an object to move.
6. work done = force × distance, work done is joules, force is newtons, distance is meters
Forces and elasticity
1. When a force acts on an object, the object may change shape. owever, there must be more than one force acting to change the shape of a stationary object A change in shape is called deformation:
  1. elastic deformation is reversed when the force is removed
  2. inelastic deformation is not fully reversed when the force is removed - there is a permanent change in shape
2. Extension happens when an object increases in length, and compression happens when it decreases in length. The extension of an elastic object, such as a spring, is described by Hooke's law
  1. force = spring constant × extension force (F) is measured in newtons (N) spring constant (k) is measured in newtons per metre (N/m) extension (e), is measured in metres (m)
3. limit of proportionality refers to the elastic limit of a material that is at the furthest point it can be stretched or deformed while being able to return to its previous shape.
4. Work is done when a spring is extended or compressed. Elastic potential energy is stored in the spring.
  1. elastic potential energy = 0.5 × spring constant × (extension)2 elastic potential energy (Ee) is measured in joules (J) spring constant (k) is measured in newtons per metre (N/m) extension (e), is measured in metres (m)
Describing Motion

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P5 - Forces

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	Created by Owen Jones about 5 years ago