Zusammenfassung der Ressource
P5 - Forces
- Scalar and Vector Quantities
- Scalar quantities only have a magnitude or size.
- Vector quantities have both magnitude
and an associated direction.
- The resultant force is a single force that has the same
effect as two or more forces acting together.
- Contact and non-contact forces
- Contact forces are forces that act between two
objects that are physically touching each other.
- An object at rest on a surface experiences
reaction force. For example, a book on a table.
- An object that is being stretched experiences a tension force. For
example, a cable holding a ceiling lamp.
- Two objects sliding past each other experience friction
forces. For example, a box sliding down a slope.
- An object moving through the air experiences air resistance.
For example, a skydiver falling through the air.
- Non-contact forces are forces that act between two objects
that are not physically touching each other.
- A magnetic force is experienced by any
magnetic material in a magnetic field.
- An electrostatic force is experienced by any
charged particle in an electric field.
- A gravitational force is experienced by any mass in a gravitational field.
- Gravity
- All objects with mass produce a gravitational
field. The more mass an object has, the greater
its gravitational field will be.
- 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.
- The weight of an object can be measured using a calibrated
spring-balance, often called a Newton meter.
- weight = mass × gravitational field strength
weight is newtons, mass is kilograms,
gravitational field strength is newtons per
kilogram (N/kg)
- Work is done when energy is transferred from one store to another.
Work is also done when a force causes an object to move.
- work done = force × distance,
work done is joules, force is
newtons, distance is meters
- Forces and elasticity
- 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:
- elastic deformation is reversed when
the force is removed
- inelastic deformation is not fully reversed when the
force is removed - there is a permanent change in shape
- 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
- 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)
- 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.
- Work is done when a spring is extended or compressed.
Elastic potential energy is stored in the spring.
- 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