Chapter 9- Forces and their effects Flashcards
How can objects interact at a distance without contact
gravitational, electrostatic and magnetic fields.
How does a magnetic field work
Has North and South poles, a magnet is surrounded by a magnetic field which pushes or pulls other magnets and things made of iron nickel or colbalt that are located within it. The earths interior acts like a magnet, the earth is surrounded by a magnetic field that affects things made of magnetic material such as compasses
How does an electrostatic field work
An electric field produced by static electric charges. Objects attract when they have opposite charges, and they repel when they have the same, the closer. The forces of attraction and repulsion are shown through electric field.
what is magnetic flux density
The amount flux passing through a unit area at a right angle to the magnetic field lines.
List some contact forces and give example
Friction, air resistance force, applied force, normal force, spring force.
A car decelerating to a stop would have friction with the road.
What are pairs of forces
For every action there is an equal and opposite reaction. This is known as Newtons 3rd law of motion. Eg- pushing a ball to the right, friction will act to the left
Difference between vector and scalar, give examples
Vector quantities have magnitude (size) and direction eg- velocity, momentum, weight.
Scalar quantities have only magnitude (size)
eg- distance, speed, power
Calculation to find moments
force x perpendicular distance
Describe situations where forces can cause rotation
torque= changes the rotation of an object.
A moment the turning effect of a force around a fixed point called a pivot. Eg- door opening around fixed hinge or spanner turning around fixed nut.
What would the principle of moments be where rotational forces are in equilibrium
The sum of clockwise moments = The sum of anti-clockwise moments
How do levers and gears transmit the rotational effects of forces
x
Explain ways of reducing unwanted energy transfer through lubrication
Double glazing in windows- gap between 2 panes of glass is filled with air and heat loss through conduction is reduced as air is a poor conductor of heat. Gap is very narrow so heat transfer by convection currents is also reduced.
Cavity wall insulation- putting insulating material between brick and the inside wall which reduces heat loss by conduction. The material also prevents air from circulating inside the cavity therefore reducing heat loss by convection.
What factors effect the turning effect
Size of force applied and the perpendicular distance from the pivot to the line of action of the force
What is a moment
Turning effect of a force around a fixed point called a pivot
what is magnetic flux density measured in
Tesla (T)
