Rotational motion Flashcards
Newton’s 2nd Law of Motion extended to a system of particles.
The total momentum of a system of particles is equal to the product of the total mass of the system and the velocity of its centre of mass.
Law of conservation of the total linear momentum of a system of particles.
When the total external force acting on a system of particles is zero the total linear momentum of the system is constant.
The trajectories of stars is a combination of: -
- uniform motion in a straight line of center of mass and
- circular orbits of the stars about the center of Mass.
UNder what conditions , torque of a body is 0?
theta = 0
r=0
A ballet dancer stretches her hands out for slowing down. It is based on which principle of conservation?
principle of conservation of angular momentum.
It it correct to say that CM of system of particles of n particles is always given by the average position vector of the constituent particles?
No, this statement is true when all the particles have the same mass.
A system is in stable eqbm. what can we say about its PE?
PE is min.
Whta shall be the effect of teh length of teh day if teh polar ice caps of earth melt?
THe K will decrease. SO MI will increase.
so inorder to conserve mvr, the angular velocity shall decrease.
- the length of teh day will increase.
why 2 propellers in helicopters?
if only one then the helicopter will start rotating in the direction opposit to the direction of rotation of teh propellers. so as to conserve angular momentum.
WHat is the kinetic energy of rolling?
When a body possess translational as well as rotation motion together it is said to be ruling. Energy associated with the body is the sum of translation and rotational kinetic energy.
Factors affecting force.
- Magnitude of force.
- Perpendicular distance of force vector from axis of rotation.
How is the angular momentum conserved in gymnasts?
When a diver dives the external force acting on the body is 0. So hence the angular momentum of teh diver is conserved. We can’t change the angular velocity directly but we can change the moment of inertia, which can impact the angular velocity. Because of teh inverse nature of angular velocity and moment of inertia, when u decrease teh moment of inertia u can increase the angular velocity.
What will happen if the earth contracts?
If suddenly the earth contracts, the mass distribution of the earth will decrease, and the radius will also decrease. So, the duration of the days on earth will not be 24 hours.
The MI decreases and angular velocity will increase thus shortening the duration of the day on earth.
Do planets change their speed when orbiting the sun?
Yes, they don’t have a circular orbit but an elliptical orbit. So, the centripetal force is provided by the radial force. As and when the radial force is present, the torque is absent. So the speed of the planet increases when they are close to the sun than when they are far away from the sun.
How does a ladder placed against the wall reach eqbm when the person is climbing?
So, at the base of the ladder, 2 forces act on it, normal force and frictional force. So, there is a torque due to these forces. If the angle formed is large enough, then the net torque and net force is 0. Hence, the ladder is in eqbm. This remains as long as the motion of the ladder remains at rest both translationally and rotationally.
