Unit 1 Test Flashcards
What is ‘The Law of Conservation of momentum’?
The total momentum of all objects before an interaction = total momentum of all objects afterwards in the absence of external forces
Netwon’s first law
An object will either remain at rest or a constant speed, unless an unbalanced force acts on it.
Newton’s second law
Fᵤₙ=ma
The acceleration of an object is directly proportional to the size of the unbalanced force and the mass of the object.
Newton’s third law
States that if object A has a force on object B, object B will exert an equal and opposite force on object A.
(For every action there is an equal and opposite reaction)
Tension
This is the force of the object being pulled being equal and opposite to the force of the object pulling.
We can calculate the tension between two objects by working out the acceleration of the whole system and then the force of one of the objects.
Fᵤₙ=ma
When we calculate F, we are calculating the resultant force. This means that we must then add on another value when calculating tension as the force must equal the weight and resultant force combined as:
resultant force= tension- weight
Tension= weight+ resultant force
Forces in a lift
When we stand on a set of scales, it is not the weight it measures but rather the equal and opposite upwards force, called the apparent weight. Tension= upwards force Weight= downwards force in a lift.
When we are in a lift, our actual weight doesn’t change but our apparent weight does.
-When the lift is stationary or moving at a constant speed, the weight is equal to the tension. -When the lift is accelerating upwards the upwards force is greater than the weight.
-When it is decelerating upwards the downwards force is greater then the tension.
-When it is accelerating downwards the downwards force is greater than the tension.
-When it is decelerating downwards the upward force is bigger than the weight.
Apparent weight in a lift
When the weight is less than the apparent weight we feel lighter. This is when the lift is:
-Accelerating down
-decelerating up
When the unbalanced force is acting down the way, we feel lighter.
When the weight is greater than the apparent weight we feel heavier. This is when the lift is:
-Decelerating down
-Accelerating up
When the unbalanced force us acting up the way, we feel heavier.
Energy transfers of ball dropping (Ep and Ek)
Initially, when the ball is at its maximum height and at rest, only potential energy will be stored in the ball as it is not moving. A soon as the ball is dropped, the potential energy immediately starts being converted to kinetic energy, and throughout the fall the amount of potential energy lost will be equal to the amount of kinetic energy gained. Just before the ball hits the ground, only kinetic energy will be stored at it is no longer as a height.
Formulas for energy
Ep=mgh (potential energy)
Ek=½mv²(kinetic energy)
Ew=fd (work done)
For the conservation of energy, the formula is initially mgh=½mv², however the masses can cancel out. This is because when we exclude air resistance, the mass has nothing to do with the time taken for the an object to fall as gravity is constant.
gh=1/2v²
This can be rearranged to get a formula for height or velocity.
equation to calculate the component of weight perpendicular to the slope
mgcosθ
equation to calculatr component of weight parallel (down) the slope
mgsinθ
the perpendicular component of the weight is equal to …
the normal force
the parallel (down) the slope component of the weight is equal to…
the friction
resultant force
the unbalanced force acting on an object
