P3.2 Using Physics To Make Things Work Flashcards
What is the relationship between forces and moments?
The larger the force the larger the moment.
How do you obtain the maximum moment?
Push at 90 degrees to the lever
When according to moments do objects not turn?
When the anticlockwise moment equals the clockwise moment.
What are levers?
Force multipliers - less force needed to get the same moment.
How do levers work according to moments?
They increase the distance from the pivot where the force is applied, meaning you need to apply less force for the same moment.
What is the centre of mass?
Where the mass of an object is thought to be concentrated.
What is a moment?
The turning effect of a force
How do you find the centre of mass in a flat shape?
- Suspend the shape and a plumb line from the same point and wait until they stop moving.
- Draw a line along the plumb line
- Do the same thing but suspend them from a different pivot point.
- Where the two lines cross = centre of mass
What happens to a freely suspended object?
It will swing until it returns to the point of equilibrium which is vertically below the point of suspension.
What two properties make an object stable?
- Low centre of mass
- Wide base
When does an object begin to tip over? (Think centre of mass)
When its centre of mass moves outside the tip of its base.
Why does the centre of mass moving outside the tip of its base make an object tip over?
The line of the action of the weight of an object is outside its base which causes a resultant moment.
What is the “time period” in pendulums?
The time taken for a pendulum to swing from one side to another and back again.
What is the rule for the time period of a pendulum?
For a given pendulum, the time period for each swing is always the same.
What is the relationship between the length of string of a pendulum and the time period?
The longer the string, the longer the time period.
Give two uses of pendulums.
- Clocks
- Playground swings
Where do you find the centre of mass in a symmetrical object?
Where the lines of symmetry cross.
What property of a liquid makes it ideal for hydraulics?
They are virtually incompressible.
What is the rule for pressure in liquids.
Pressure in a liquid is transferred equally in all directions.
What is the rule for force in liquids?
A force applied in one point will soon be transmitted to other points.
What do hydraulic systems do?
Act as force multipliers.
Describe a hydraulic system.
- The system has two pistons, the first has a smaller cross sectional area.
- Pressure is exerted in the liquid in the 1st piston using a small force over a small area.
- The same pressure is transmitted to the 2nd piston which has a larger surface area so there will be a larger force (force = pressure x area)
Where are hydraulic systems used?
- Car braking systems
- Hydraulic car jacks
- Manufactoring
Where do objects travelling in a circle move?
They accelerate towards the centre of the circle.
Why do objects travelling in a circle accelerate?
Their direction is constantly changing so their velocity (not speed) is constantly changing meaning they accelerate towards the centre of the circle.
What is the centripetal force?
The resultant force that directs an object towards the centre of the circle.
Name 3 forces that provide centripetal force.
- Gravitational force
- Friction
- Tension
Give an example of centripetal force caused by friction.
A car going round the bend - friction between the tyres and the road causes a centripetal force.
Give an example of centripetal force caused by tension.
A bucket on a rope - caused by tension in the rope.
What factors affect centripetal force?
- Mass of the object
- Speed of the object
- Radius of the circle
If mass —–, speed —— or radius —–, centripetal force will increase.
1) increases
2) increases
3) decreases
