Dynamics Intro

Dynamics: The branch of Physics which deals with the causes of motion

Force: A force is a push or pull

Forces are measured in Newtons

Force is a vector quantity.

FBD: An FBD is a simple diagram of an object showing all the forces acting on the object.

e.g.Free fall Book on a desk

Pushing a lawn mower:

Reviewing Newton's 3 Laws

1. State each of Newton's 3 Laws and give 2 good examples of each
2. What is inertia?
3. Add these definitions to your notes::
   1. A State of equilibrium - a state in which all forces are balanced ( Newton's first law applies)
   2. Static equilibrium - same as part "a" but the object is at rest
   3. Dynamic equilibrium -same as part "a" but the object is moving

Dynamics Intro Problems

1. Assume an 8-passenger Learjet has a force of gravity of 6.6 x10⁴N [down] acting on it as it travels at a constant velocity of 6.4 x10²km/h [W]. If the forward thrust provided by the engines is 1.3 x10⁴N [W], determine:
   1. the upward lift force on the plane
   2. the force due to air resistance on the plane

1. Which of the following italicised objects are not examples of Newtons First Law; explain your choice:
   1. A cat-food can moves at a constant velocity on a conveyor belt in a factory.
   2. A skydiver falls vertically at terminal velocity
   3. A rubber stopper is tied to the end of a string and swings back and forth as a pendulum.
   4. A shopper stands on an escalator, halfway between floors in a department store and rises at a constant velocity.
   5. A ball travels with projectile motion after leaving a pitchers hand.

1. A child is trying to push a large desk across a wooden floor. The chile is exerting a horizontal force of magnitude 3.8 N, but the desk is not moving. What is the magnitude of the force of friction acting on the desk?

1. A snowboarder is travelling at a high speed down a smooth, snow covered hill. The board suddenly reaches a rough patch, encountering significant friction. Use Newtons first law to describe what is likely to happen to the snowboarder

1. You are sitting on a bus that is travelling at a constant velocity of 55 km/h [N]. You toss a tennis ball straight up and it reaches a height that is level with your eyes. Does the ball hit you in the face? Explain your answer

1. The following sets of forces are acting on a common point. Determine the additional force needed to maintain static equilibrium:
   1. 265 N [E], 122 N [W]
   2. 32 N [N], 44 N [E]

1. Explain the danger of storing heavy objects in the rear window space of a car.

1. A horizontal force is applied to a hockey puck of mass 0.16 kg initially at rest on the ice. The resulting acceleration of the puck has a magnitude of 32 m/s² . What is the magnitude of the force? Ignore friction.

1. A fire truck with a mass of 2.95 x10⁴ kg experiences a net force of 2.42 x10⁴ N [fwd]. Determine the acceleration of the truck.

1. A 7.27 kg bowling ball travels at 5.78 m/s [W] strikes a lone pin straight on. The collision lasts for 1.2 ms and causes the balls velocity to become 4.61 m/s [W]. Determine the net force acting on the ball during the collision.