Forces in balance
- Created by: adwoaka9714
- Created on: 18-03-19 19:33
Vectors and Scalars
Displacement distance in a given direction
Vector a quantity that has a magnitude and direction
- Weight
- Velocity
- Acceleration
Scalar a quantity that only has a magnitude
- Temperature
- Speed
- Energy
The direction of the arrow shows the direction of the vector quantity
The length of the arrow represents the magnitude of the vector
Forces between objects
Newtons Third Law when 2 objects interact with each other, they exert equal and opposite force on each other
Non-Contact Forces forces that can be exerted between objects without them being in contact with one another
- Gravity- A gravitational force comes between all masses
- Manets- A magnetic force acts between magnetic poles
- Charges- Exert electrostatic forces on each other at a distance
Contact Forces forces that can be exerted on each other due to them being in contact
Normal force
- acts upwards in opposition to the object
Force of friction
- acts in opposition to the pushing force that is trying to change its motion. Force always acts to slow a moving object down
Resultant Forces
Resultant forces The single force that would have the same effect as all the other forces acting on the object
Resultant forces determine whether a body will be stationary ,moving at constant speed or accelerating
Newtons First Law the forces acting on an object are balanced, the resulatant force on the object is zero
- if the object is at rest it is stationary
- if the object is moving it keeps moving with the same speed and in the same direction
Unbalaned Forces
When the resultantb force is not zero, the forces acting on the object are not balanced.The movemrnt of the object depends on the size and direction of the resultant force
- Resultant force is equal to the difference between 2 forces
- Resultant forces is in the direction of the larger force
Sometimes forces forces act at right angles to each other.The resultant force can then be found from a scale diagram using pythagorus therom
Moments at work
Moment of a force a measure of the turning effect of the force on ana object
Moments can be increased by: increasing the force
using a spanner with a longer handle
Moment,M(Newton meters,Nm) = Force,f(Newtons,N) x Distance,D(Metres,M)
The distance is the perpendicular distance from the line of action of the force x to the pivot
Load the weight of the object
Effort the force the person applies to the crowbar
Force Multipiler are tools that help you Amplify your effort to produce more output
Sum of clockwise moments = Sum of anticlockwise moments
Levers and gears
Lever used as a force multiplier exerts a greater force than the force applied to the lever by the effort
Gear used to change the moment of a turning effect
When a low gear is chosen:
A small gear wheel driven by the engine shaft is used to turn a large gear wheel on the output shaft. So the output shaft turns slower than the shaft engine
The turning effect of the output shaft is greater than the turning effect of the engine shaft
Low gear gives low spped and a high turning effect
When a high gear is chosen:
A large gear wheel driven by the engine shaft is used to turn a small gear wheel on the poutput shaft. So theoutput shaft turns faster than the engine shaft, so the car can move at a higher speed
But the force of the smaller gear wheel acts nearer to its shaft than the force of the larger gear wheel acting on its shaft. So the turning effect of the output shaft is less than the turning effect of the engine shaft
High gear gives high speed and a low turning effect
Centre of mass
Centre of mass of a object the point where its mass can be thought of as being concentrated
The centre of mass of a uniform ruler is at its midpoint
When an object is freely suspended it comes to rest with its centre of mss directly underneath the point of suspension
The centre of mass of a symmetrical object is along the axis of symmetry
Moments and equilibrium
Point of moments
If an object at rest doesnt turn The sum of clockwise moments about any point = The sum of anticlockwise moments abou that point
All the forces acting on an object that dont pass through a fixed point can turn an object about that point
The direction of the force and the position of the fixed point determines whether the moment acts clockwise or anticlockwise
To calculate the force needed to stop an object turning we use the principle of moments. We need to know all the forces that dont act through the pivot and their perpendicular distances from the line of action to the pivot
The parallelogram of forces
Parallelogram of forces a scale diagram of to vectors
The pallelogram of forces is used to find the resultant of two forces that do not act along the same line
The resultant is diagonal of the parallelogram that starts at the origin of two forces
Resolution of forces
Resolving a force fimding perpendicular components that have a resultant force that is equal to the force
To resolve a force in two perpendicular directions, draw a rectangle adjacent sides along the two directions so that the diagonal represents the force vector
Key conditions object to be in equilibrium are:
- The resultant force on the object is zero
- The forces acting on the object have no overall turning effect
An object at rest is in equilibrium because the resultant force is zero
To work out if an object is in equilibrium:
- If the liness of action of the forces are parallel, the sum of the forces in one direction must be equal to the sum of forcse in the opposite direction. This means that the resultant force on the object is zero
- If the lines of action of the two forces are not all parallel, the forces can be resoved into two components along the same perpendicular lines. The components along each line must balance out if the resultant force is zero
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