newton's laws of motion + momentum Flashcards
what is newtons first law of motion
an object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force
what does the term constant velocity mean
speed and direction stay the same
what is a resultant force
one force which has the same affect as all forces acting on a body
what is newtons third law of motion
when two object interact they exert an equal and opposite force on each other
F1=-F2
F2 is negative as the force is going in the opposite direction
what are the rules about newtons third law of motion
forces acting on the interacting objects are always the same type - electrostatic, magnetic or gravitational
forces will act on different objects - both forces never act on the same object
e.g. gravitational force exerted by the earth - your weight, is equal and opposite to the gravitational force that you exert on the earth
what does the momentum of an object depend on
it mass and its velocity
what is the equation for momentum
momentum = mass x velocity
p=mv
what is the SI unit of momentum
kgms^-1
is momentum a vector or scalar quantity
vector - product of a scalar (mass) and a vector (velocity)
what is the principle of conservation of momentum
alternative way of looking at newtons second law
for a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system
total momentum before and after the collision is the same
when object interact what is transferred between the objects
momentum and kinetic energy
why is there zero momentum when a gun is fired
gun recoils when a bullet is fired
total momentum of system remain the same and is equal to zero
momentum of the gun and the momentum of the bullet have the same magnitude but act in opposite directions
how would you investigate momentum
use a linear air track - minimises the friction between the gliders and track
trolleys and a horizontal runway - runway has to be at an angle to account for friction - angle is large enough so the trolley is just moving i.e. there is no friction
velocity of each object determined with a motions sensor and a laptop, light gates and a digital timer - measure the time taken to cover a known distance
what are perfectly elastic collisions
total kinetic energy conserved
scalar so adds up no matter that direction
momentum is conserved
total energy is conserved
what are inelastic collisions
kinetic energy is not conserved - energy will transformed into other forms e.g. heat, sound
momentum conserved
total energy conserved
what is a completely inelastic collision
the colliding objects stick together after the impact
what is newtons second law of motion
the net resultant force acting on an object is directly proportional to the rate if change of its momentum and in the same direction
net force directly proportional to rate of change of momentum
(m1v1-m1u1)/t=-(m2v2-m2u2)/t
cancelling t and rearranging
m1u1+m2u2=m1v1+m2v2 - therefore when no external force is applied momentum is conserved
F directly proportional p/t
F=(kp)/t
F=p/t
what is the equation for newtons second law of momentum
F=p/t
how do you derive newtons second law of momentum equation F=p/t
F=ma
a=(v-u)/t
F=(mv-mu)/t
F=(mv)/t
F=p/t
when can you use F=ma to work out momentum
the mass of the object remains constant during the period of acceleration
why is momentum conserved in collisions
two interacting objects each experience an equal but opposite force
the net force actin on the objects in a closed system is 0
according to newtons second law p/t=0
the change in momentum of both objects must be zero therefore the total momentum of the objects does not change - momentum is always conserved
why does newtons second law lead to reducing impact forces
increase time taken to stop reduces the rate of change of momentum which decreases the impact force
what is an impulse of a force
the product of force and the time for which this force acts on an objects
the change in momentum
the area under the force time graph - the product of force and the time for which the force acts - momentum
how does the impulse of a force link to newtons second law of motion
net force = rate of change of momentum
F=p/t
F x t = p
the product of force and time is equal to the chane on momentum
