Chapter 11: Forces Flashcards
What is the difference between vector and scalar quantities?
Vector quantities need direction for them to be valid, whereas scalar are just numbers.
Name some everyday forces
Weight, friction, air resistance, drag, engine force, lift, upthrust
What is the resultant force?
The single force that can replace a set of forces giving the same motion
What type of force is friction?
Friction is a force that opposes motion.
What equation links resultant force, mass and acceleration?
force = mass x acceleration
What is the equation for weight?
weight = mass x gravity
What is the unit for force?
Newtons
What is the unit for acceleration?
ms^-2
What is the unit for gravity?
N/kg
What is the unit for mass?
kilograms
What is the stopping distance?
thinking distance + braking distance
What is the thinking distance?
The distance traveled in the time between seeing the car and putting your foot on the brake
What is the braking distance?
The distance travelled in the time between your foot being on the brake and the car stopping.
Give some examples of factors that can affect the thinking distance.
Being drunk, ill, or on drugs; fog or other weather making it harder to see
Give some examples of factors that can affect the braking distance.
icy roads, worn tyres, worn brakes
Explain the relationship between the two opposing forces during terminal velocity
At terminal velocity, the two opposing forces are balanced.
Give some examples of vector quantities.
velocity, acceleration, displacement
Give some examples of scalar quantities.
speed, distance
What is the motion of an object with a resultant force of zero?
Newton’s First Law: Every object continues in a state of rest or of uniform motion unless there is a resultant force acting.
What is the motion of an object with a positive resultant force?
The object has started moving or changing speed - it is going to the right
What is the motion of an object with a negative resultant force?
The object has started moving or changing speed - it is going to the left
Explain the motion of a parachutist in terms of resultant force, drag and weight
When the parachutist first jumps out of the plane, there is no upward force, and so there is a large resultant force downwards, so they accelerate quickly. The air resistance increases as the parachutist’s speed increases, and so they accelerate slowly. The air resistance and weight are balanced and so the parachutist travels at a constant high speed, and has reached terminal velocity. The parachutist opens their parachute, and the large air resistance causes them to decelerate quickly. The air resistance decreases as the parachutist’s speed decreases, and so they decelerate slowly. The air resistance and weight balance again, and so the parachutist reaches a new lower terminal velocity.
How to investigate acceleration due to gravity in an experiment using a light gate?
Drop the picket fence (alternating opaque and transparent sheet) through the light gate; results will be recorded on the computer via the data logger
What is Newton’s Second Law?
The effect of a resultant force depends on how big the force is, the direction in which it is acting and the mass of the object.
How to investigate acceleration due to gravity in an experiment using ticker tape?
Attach ticker tape to a mass and drop the tape through the machine. Measure distance between two dots on the ticker tape for two spaces. Find the velocity for each pair, and from there, find the acceleration.
