P2.2 Flashcards
State one way in which the force of gravity is different to the electrostatic force.
- The force of gravity is only attractive.
- The electrostatic force can be either attractive or repulsive, depending upon whether there are unlike or like charges interacting respectively.
What is a field
the region where electrical/magnetic/mass bodies experience a force.
Newtons 3rd law
When two bodies interact, they exert a force upon each other that is equal in size, but opposite in direction
Explain why the force of water resistance is greater than the force of air resistance
As water is more dense than air, it contains more particles (mass) than air, thus more particles collide and interact, exerting a greater force of resistance.
How to calculate resultant force if they act 90° to each other
- draw a force triangle
- join two forces head to tail
- resultant force is the hypotenuse
How to resolve a force
Make a triangle out of the force
- the force itself is the hypotenuse
- its components are the sides
- use trig identities
Resolve this force
Newton’s first law
A body will remain at rest, or continue to move at a uniform velocity, unless acted upon by a resultant force
What is inertia
a measure of how difficult it is to change the velocity of a body.
How does mass effect inertia
greater the mass of a body, the greater its inertia…… the more difficult it is to change its velocity… the more difficult it is to accelerate the body.
Describe and explain what happens to a person when they are standing on a bus that suddenly brakes.
Both the bus and person are moving at the same velocity before the bus brakes.
After braking, the bus comes to rest, but by Newton’s First Law, the person continues to move at the same velocity as no resultant force has yet acted on the person.
Thus, the person is seen to “jolt” abruptly forwards.
Newtons 2nd law (definition)
The acceleration experienced by a body is directly proportional to the resultant force acting upon it, and in the same direction as
Newton’s second law (formula)
F = ma
What is acceleration
ACCELERATION IS THE RATE OF CHANGE OF VELOCITY OF A BODY
Acceleration formula
a = ((𝐯−𝐮))/𝐭
What is terminal velocity
The velocity at which a body falls through a medium, when the drag acting on the body is equal to its weight.
Parachute velocity - Time Graph
Explains what happens when a parachutist jumps out of a plane (6 marks)
- When parachutist jumps, the drag force acting is small so parachutist experiences large acceleration, due to the force of his weight
- As his speed increases, the drag force acting on him will increase so the resultant force on him will decrease and his acceleration will decrease
- ## Eventually the drag force will equal the weight. Acceleration is now zero and the speed is constant - this is known as Terminal Velocity.
How to resolve a box on a slope force
Don’t understand this
Calculate the size of the normal contact force of a block on a ramp if the weight of the block is 2N, and the angle between the weight and the component of weight that balances it is 30°.
I UNDERSTAND NOW
Momentum equation
p = m x v
Momentum (Kgm/s) = mass x velocity
Units of momentum
Kgm/s
What is the law of conservation of momentum
The total momentum before an event is equal to thetotal momentum after the event.
If a stationary body hits a moving body…
the two bodies will move off together.
Work done equation
W = F x d
A builder pushed a wheelbarrow of weight 200N up a slope(at constant velocity), a distance of 15m, and height 10m.
a) much work did she do against gravity?
b) If the total work done was 2500J,how much friction was acting?
a) Doing work against gravity, means opposing the weight, which only acts straight down…W = F x d = 200N x 10m = 2000J
B) (total work) = (work done against gravity) + (work done against friction)
=> (work done against friction) = (total work) – (work done against gravity)=> (work done against friction) = 2500J – 2000J = 500J
W = F x d=> F = W/d = 500J/15m = 33N (2 s.f.) of FRICTION
FRICTION = FORCE
What is power (definition)
Power is the rate of energy transfer.
What is power (equation)
P = E / t
What is the unit of power
Watt
= 1 Watt is 1 Joule of energy transferred in 1 second.
= 1 kilowatt, kW is 1000 Joules of energy transferred in 1 second.
