P3 - Using Physics Flashcards
What is the moment of a force?
A measure of the turning effect of a force on an object.
How is the moment of a force calculated?
force x perpendicular distance from the line of action of the force to the pivot
Give two ways in which the moment of a force can be increased.
- Increase the force
- Increase the perpendicular distance
What is the centre of mass of an object?
The point where its mass is concentrated.
Where is the centre of mass of an object that is suspended from a fixed point?
The centre of mass is directly beneath the point of suspension.
Where is the centre of mass of a symmetrical object?
Along the axis of symmetry.
What is the relationship between the moments of the forces acting on an object that isn’t turning?
The sum of anticlockwise moments = The sum of clockwise moments (ie. W1d1 = W2d2)
How is the weight of the first object calculated with moments?
W1 = W2d2 / d1
Give three ways in which an object can be made more stable.
- Increasing the width of the base.
- Making the centre of mass lower.
- Bolting the object to the floor.
What will make a body topple over when tilted?
If the line of action of its weight is outside its base.
What are the moments of the forces when an object topples over?
The resultant moment about the point of turning is not zero.
What is pressure?
Force divided by the area which the force acts on.
What is the unit of pressure?
The Pascal, Pa. (1 N/m2)
What happens to the pressure in a fluid?
The pressure acts equally in all directions.
How does a hydraulic pressure system work?
- Hydraulic fluid into the upper or lower part of a chamber to make the piston move in or out of the cylinder.
- The force exerted is transmitted to other parts of the system.
Why are liquids used in hydraulic systems?
- Liquids are virtually incompressible so the volume doesn’t change.
- The whole force can be transmitted to the other parts.
How does a hydraulic car jack work?
- The handle being pressed down forces hydraulic fluid out of a narrow cylinder into a wide cylinder.
- The pressure of the fluid forces the piston in the wider cylinder outwards.
- The piston forces the pivoted lever to raise the car.
Why is the second force in a hydraulic car jack greater?
The area of the piston is greater.
How can an object moving at a constant speed be accelerating?
If the motion is circular.
Why is an object moving in a circular motion said to be accelerating?
- Velocity is dependent on direction as is acceleration.
- The velocity is changing as the direction is changing.
What is centripetal acceleration?
The acceleration towards the centre of the circle of an object that is moving round the circle.
What does the centripetal force depend on?
- Mass
- Speed
- Radius of the circle
What is centripetal force?
The name of a resultant force acting on a circle moving round an object.
What affects the time period of a pendulum?
Its length.
How is the time period of a pendulum measured accurately?
The average time of 20 oscillations.
How is a playground swing different to a pendulum?
- Friction at the top of the swing slows it.
- Air resistance slows it.
What is the equilibrium position of a pendulum?
The point at which the pendulum is fastest and nearest the ground.
What is the amplitude of an oscillating object?
The distance from the equilibrium position to its highest point.
What is the time period of a pendulum?
-The time to one of the highest points and back.
or
-The time between successive passes in the same direction through the equilibrium.
