P5 Forces Flashcards
What is force?
Vector quantity (have a magnitude and a direction)
Examples of physical quantities that are vector quantities
-Force, velocity, displacement, acceleration, momentum
Examples of physical quantities that only have magnitude and no direction
Scalar quantities: Speed, distance, mass, temperature, time
What usually represents a vector?
- An arrow
- The length shows the magnitude
- The direction shows the direction of the quantity
Contact force
Forces that make contact (e.g. pushing something)
Non contact force
Forces that don’t make contact (magnetic force, gravitational force)
What is gravitational force?
The force of attraction between masses
Mass
The amount of ‘stuff’ in an object
Weight
The force acting on an object due to gravity
What affects weight?
The strength of the gravitational field at the location of the object
Centre of mass
A point at which you assume the whole mass is concentrated
How is weight measured?
A calibrated spring balance
Are mass and weight directly proportional?
Yes
Weight (N) = ?
Mass (kg) * GFS (N/kg)
What is resultant force?
The overall force on a point or object
What are parallel forces?
The forces are all along the same line (you can add and subtract the forces to find the resultant force)
What is work done in terms of distance and force?
When a force moves an object through a distance, energy is transferred and work is done on the obejct
Work done eq (force and distance)
Force * Distance
What happens when the resultant force is 0?
The object is equilibrium (the 3 forces will make a triangle)
Why should we split forces into simpler components?
Because some forces are at difficult angles to work with
Distance
How far an object has moved (scalar quantity)
Displacement
A vector quantity which measures the distance in a straight line from an object’s starting point to finishing point
Speed
How fast you are going
Velocity
The speed in a given direction
distance travelled eq (speed and time)
Distance = speed / time
Walking speed
1.5 m/s
Running speed
3 m/s
Cycling speed
6 m/s
Car speed
25 m/s
Train speed
30 m/s
Plane speed
250 m/s
Acceleration
The change in speed in a certain amount of time
Deceleration
Negative acceleration
Uniform acceleration
The constant accelertaion
uniform acceleration equation
v^2 - u^2 = 2as
How to work out speed in distance time graphs
Gradient
Flat parts on distance time graphs
Stationary
Straight parts on distance time graphs
Steady speed
Curves on distance time graphs
Represent acceleration and deceleration
Steepening on distance time graphs
Speeding up
Levelling off on distance time graphs
Slowing down
Velocity time graph
Shows how an object’s velocity changes as it travels
Gradient on velocity time graph
Acceleration
Flat sections on velocity time graph
Travelling at a steady speed
Steeper the gradient on velocity time graphs
The greater the acceleration or deceleration
Uphill sections on velocity time graphs
Acceleration
Downhill sections on velocity time graphs
Deceleration
How to work out distance travelled in a time interval in a velocity time graph
The area
Friction
The opposite force in direction to movement
How to reduce friction
Use a lubricant
Drag
The resistance you get in a fluid (gas or liquid)
Example of drag
Air resistance
What can be done to reduce drag
Keeping the shape of the object streamline
Examples of objects that increase drag
Parachutes
Terminal velocity
When an object has reached its maximum speed and will fall at a steady speed
Why is there terminal velocity?
- Force of gravity is much more than frictional force, therefore the object accelerates
- As the speed increases, friction builds up
- This gradually reduces the acceleration until eventually the friction force is zero
What usually affects terminal velocity
- The shape and area of the object
- Objects with large surface areas have lower terminal velocities
Newton’s first law
- If the resultant force on a stationary object is zero, the objects will remain stationary.
- If the resultant force on a moving object is zero, it’ll just carry on moving at the same velocity
Newtons second law
Newton’s second law states that the acceleration of an object depends upon two variables – the net force acting on the object and the mass of the object.
Resultant force eq (acceleration and mass)
f = m*a
Inertia mass
Measures how difficult it is to change the velocity of an object
Inertia mass on newton’s second law
The mass (m = f/a)
Newton’s third law
When 2 objects interact, the forces they exert on each other are equal and opposite
Momentum
A vector quantity resultant from mass and velocity
Momentum equation
mass (kg) * velocity (m/s)
Conservation of momentum
The total momentum before the event is the same as after the event in a closed system
