Paper 2 Forces Flashcards
What is a moment
The turning effect of a force
Moment=
Force x distance moved
Clockwise moments=
Anti-clockwise moments
W1 x D1 = W2 x D2
How is the seesaw an example of the principles of moment
This states that for an object in equilibrium the sum of all clockwise moments about any point is equal to the sum of all anti-clockwise moment about that point
What is the centre of mass of an object
The point at which the mass may though to be concentrated
How can the centre of mass be found for symmetrical objects
Always lies along the line of symmetry of that object, if more that 1 line of symmetry, it’s where the lines cross
How to find the centre of mass of an object in suspension
If you suspend object then release it it will soon come to rest. The centre of mass will be directly below the point of suspension. The object is said to be in equilibrium
How do you find the centre of mass in an irregular shape
Shape is hung from a point and plumb line used to draw vertical line downwards from that pivot. The COM is somewhere along that point. This is repeated with the shape hanging from different points. Where they all intercept is the COM
The stability of an object is affected by 2 factors
The width of the base of the object
The height of its centre of mass
What is stable equilibrium
The centre of mass is raised as it is tilted (it tilts then falls back to the original position)
What is unstable equilibrium
The centre of mass is lowered as it’s tilted (it tilts then falls over)
What is neutral equilibrium
The centre of mass stays at the same level if it is pushed (it rolls)
How do levers work
The greater the length of the lever from the pivot to the applied force, the easier it would be to lift the mass
What is a force multiplier
A machine which allows small effort (input force) to move a larger load (output force);
What is the mechanical advantage of a machine
The number of times the load moved is greater than the effort used
Mechanical advantage=
load/effort
In a force multiplier the mechanical advantage is…
Greater than 1
In a distance multiplier the mechanical advantage is…
Less than 1
What is the mechanical advantage of a lever if the distance from the pivot is 3x greater than the distance from the pivot to the load
Mechanical advantage is 3, the load is 3x heavier than the effort
What is a distance multiplier
Take small movement of the effort and multiply it into a large movement of the load
How are bicycles examples of distance multipliers
The gears of a bike are designed so that slow movement of the pedals produces a much faster rotation of the wheels
Why do you use a low gear uphill in a car
Want a force multiplier, want output more than input
Why do you use a higher gear downhill in a car
Want a distance multiplier, want output smaller than input
If a bottle was filled with water and had holes at different heights, what would happen
The deeper the whole, the higher the pressure so the water is pushed with a greater force so has a bigger horizontal range
Pressure =
Weight of liquid/area
Pressure depends on 2 things:
How much force is applied How big (or small) the area on which the force is applied
Equation for hydraulics
Force A/Area A = Force B/Area B
Force B/Force A = Area B/Area A
What does a smaller force on piston A mean (hydraulics)
Smaller force on piston A will produces a larger force on piston B because the pressure of the liquid is constant. This acts as a force multiplier
What is the atmosphere
A relatively thin layer of air around the Earth
The greater the altitude…
The less dense the atmosphere and the lower the atmospheric pressure because there is less air above the surface so there is smaller weight of air acting on the surface since p=F/A
How is upthrust created
The bottom surface of an object submerged in a liquid experiences a greater pressure than the top surface, creating a resultant force called upthrust
When do objects float
When its weight=upthrust
If the density is less than the fluid
When the weight of the object= weight of fluid displaced
What is momentum
Any object that moves has momentum
What is the formula for momentum
Momentum = mass x velocity (p=mv)
What are the units for momentum
kgm/s
Why is a ball harder to stop if it has a large mass and is moving at a high velocity
Because there’ll be a greater force exerted on a person’s hand and the person will have to exert an equal and opposite force on the ball to stop it, the greater the force required, the harder it’ll be to stop
In any collision or explosion momentum is…
Conserved (provided there are no external forces having an effect e.g. friction or gravity)
Force =
Change in momentum / time
