11629920
Description
Mind Map by Kieran Lancaster, updated more than 1 year ago
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Created by Kieran Lancaster
over 6 years ago
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Chapter 7 - Laws of motion and
momentum
- Newton's 1st and 3rd Laws of
motion
- 1st Law - An object will remain at rest or continue to move with consant velocity unless
acted upon by a resultant force (Cylcist has drag, weight and n.c.f, but no acceleration)
- 3rd Law - When two objects interact, they exert equal and opposite forces on
each other (e.g Normal contact force, electrostatic repulsion)
- Four types of forces. Strong and weak nuclear force have very
little range, and little effect. There is the gravitational force of
attraction between masses, and the electrostatic repulsive forces,
which occurs in the atomic electron clouds.
- 1st Law - An object will remain at rest or continue to move with consant velocity unless
acted upon by a resultant force (Cylcist has drag, weight and n.c.f, but no acceleration)
- Momentum
- SI unit is Kgmsˉ¹ It's a vector quantity, as it's a product
of a scalar (mass) and vector (velocity)
- Principle of conservation of momentum - In a closed system (there are no
external forces acting on objects), momentum is conserved
- This means total momentum before and after a collision is the same. This may
mean total momentum is zero, e.g a bullet recoilling once fired. Both have the
same magnitude of momentum but in opposite directions
- Momentum can be investigated using gliders on an air track, or trolleys on a horizontal runway.
Velocity can be measured with light gates, or a stopwatch and time to cover a known distance
- Momentum and Total energy are conserved in all collisions.
Inelastic collisions are when Kinetic Energy is not conserved,
whereas elastic collisions are when Kinetic Energy is conserved
- SI unit is Kgmsˉ¹ It's a vector quantity, as it's a product
of a scalar (mass) and vector (velocity)
- Newtons 2nd Law of motion
- The net (resultant) force acting on an object is directly proportional to the rate
of the change of momentum, and is in the same direction
- Net force ∝ rate of change of momentum, therefore:
- F=ma is just a special application of newtons second law, when
the mass of the object remains constant during acceleration
- The net (resultant) force acting on an object is directly proportional to the rate
of the change of momentum, and is in the same direction
- Impulse
- Rearranging newtons second law,
the product of force and time is
equal to change in momentum
- Impulse is the product of force and the time for which the
force acts on the object, units Ns or Kgmsˉ¹
- The area under a force time graph
is equal to the change in
momentum, even if force is
changing
- Rearranging newtons second law,
the product of force and time is
equal to change in momentum
- Collisions in two dimensions
- Since linear momentum is conserved in all directions, vector
triangles can be used to resolve vectors and solve problems
- In the x direction, total initial momentum = total final momentum
- m₁v₁ = m₁v₁cosθ + m₂v₂cosα
- m₁v₁ = m₁v₁cosθ + m₂v₂cosα
- In the y direction, total initial momentum = total final momentum
- 0 = m₁v₁sinθ₁ + m₂v₂sinα
- 0 = m₁v₁sinθ₁ + m₂v₂sinα
- Since linear momentum is conserved in all directions, vector
triangles can be used to resolve vectors and solve problems
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