Dynamics Flashcards
What are non-contact forces
Forces that do not require objects to be in contact to exist.
Examples: gravitational force, electrostatic force, magnetic force
What are contact forces
Forces that exists between objects that are in contact
Examples; Friction, air resistance, normal force, tension
What is the formula for gravitational field strength
g = W/m where g is field strength, W is weight in newtons, m is mass in kg
When a spaceship travels between earth and moon, why does it experience zero weight at a point in time while travelling
The gravitational field of the Earth and Moon cancel each other
What apparatus should be used to measure mass
Beam balance or calibrated electronic balance
What apparatus should be used to measure weight
Spring balance
What is the equation for force
F = ma
What is Newton’s First Law of Motion
Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it
What is Newton’s Second Law of Motion
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The object accelerates in direction of net force
The larger the mass, the ___ inertia the object will have
More
Using ideas about inertia, explain why people should wear seatbelts
If a driver suddenly applies the brakes, he will continue to move forward due to his inertia
What is Newton’s Third Law of Motion
If body A exerts force AB on body B, the body B will exert and equal and opposite force BA on body A
What are some positive effects of friction
Walking, slowing down objects, grip –>prevents skidding or to hold a pen
What are negative effects of friction
Wear and tear, unwanted slowing down or stopping of motion, generates unwanted heat
How to reduce friction
Use smooth and polished surface
Use wheels and rollers
Use ball bearings around axles
Use lubricants
Use air as cushion
Adopt a streamline shape
How do objects fall with air resistance
On earth, falling objects always experience air resistance. Air resistance increases as speed of falling object increases. At point where air resistance equals weight, there is zero acceleration and object falls with constant velocity known as terminal velocity
Describe skydiver falling with air resistance with parachute first closed
When skydiver slides out from plane, only force acting is gravitational force and initial downward acceleration is uniform at 10 ms-2. As he falls, air resistance opposing motion starts to increase, net force downwards decreases and falls at decreasing acceleration. Air resistance continues to increase until it is equal to weight and he falls with zero acceleration and terminal velocity
Describe skydiver falling with air resistance when parachute opens midway through fall
Skydiver opens the parachute, larger surface area of parachute gives rise to larger air resistance. Net force is upwards and skydiver decelerates. Skydiver slows down until air resistance decreases until balancing his weight. A lower terminal velocity is reached and skydiver continues to the ground at constant velocity
How does greater weight affect terminal velocity
Larger weight needs larger air resistance to balance its weight. Accelerates for longer duration and larger terminal velocity, so reaches ground in shorter time due to larger average speed
How does larger surface area affect terminal velocity
Object that has larger surface area traps more air molecules underneath as it falls. Air resistance increases at faster rate but final air resistance is equal regardless of surface area as weight is equal. Accelerates for shorter duration and smaller terminal velocity, so reaches ground in longer time due to smaller average speed
Explain why ball experiences constant acceleration during free fall through air (no air resistance)
As there is no air resistance, the net force, the ball’s weight, remains constant and thus acceleration remains constant with mass.
