5.1 Forces Flashcards
Scalar and vector quantities
Scalars are quantities that have only a magnitude.
Examples include distance, time, speed, mass.
Vector quantities have both a magnitude and a direction.
Examples include displacement, velocity, acceleration.
Forces
A force is a push or a pull that acts on an object when it interacts with another object. All forces between objects are either:
Contact and non - contact
When an object experiences a force it can deform or accelerate.
Contact forces
Contact forces happen when two objects are physically touching.
Friction - sliding across a surface.
Lift - upward force on a wing.
Thrust - propulsive force of an engine.
Up thrust - upwards force when an object is in a fluid
Drag - acts against objects moving through a fluid.
Tension - is described as a pulling force transmitted by a string or similar object.
Normal contact force - push or a pull.
Non - contact forces
Non-contact forces happen when objects are separated (not touching).
Weight - force due to gravity.
Magnetic - force between magnetic objects.
Electrostatic - force between charged objects.
Gravity
Weight is the force acting on an object due to gravity.
Weight = mass x gravitational field strength
W = mg
Mass
The mass of an object is a measure of the amount of matter it contains. The mass of an object is constant. It is the same on Earth, on the Moon and in space.
Centre of mass
Although the mass of an object is spread out across its body, it is possible to find a single point where all of the mass appears to be. This point is called the object’s centre of mass.
The centre of mass is the point through which an object’s weight appears to act.
If an object is hung from a string, it will hang with its centre of mass directly below the point that it is hung from.
An object will fall over if its centre of mass is outside its base.
An object will fall off a surface if its centre of mass isn’t over the surface.
Resultant force
A resultant force is a single force that describes all of the forces operating on a body.
When many forces are applied to an object they can be combined (added) to produce one final force which describes the combined action of all of the forces.
This single resultant force determines:
The direction in which the object will move as a result of all of the forces.
The magnitude of the final force experienced by the object.
The resultant force is sometimes called the net force.
Balanced and unbalanced forces
Balanced forces mean that the forces have combined in such a way that they cancel each other out and no resultant force acts on the body.
Unbalanced forces mean that the forces have combined in such a way that they do not cancel out completely and there is a resultant force on the object.
