P5 (part 3) Flashcards
What is Newton’s First Law?
if the resultant force acting on an object is zero ( or if there’s no resultant force) and:
- the object is stationary, the object remains stationary
- the object is moving, the object continues to move at the same speed and in the same direction. so the object continues to move at the same velocity
What does the force “T” represent?
tension
Explain why an object being swung in a circle at a constant speed , does not have a constant velocity
although the object’s speed is constant, the direction is always changing , which means the velocity is always changing
What is inertia?
the tendency of an object at rest to stay at rest or moving object to continue moving
Give an example of a situation where an object has a large inertia
rugby player with the ball has a lot of mass (plus his team mate adding mass to him). He has alot of inertia
What is Newton’s Second Law?
the acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object
OR YOU CAN SAY:
If the force on an object is doubled, the acceleration will also double. but if the mass of an object is doubled, the acceleration will halve
What would the equation be for force?
force (N) = mass (kg) x acceleration (m/s2)
f = m x a
What is the definition of inertial mass?
is the ratio of force over acceleration
What symbol do we use to mean ‘approximate’?
≈
What is the typical approximate values of speed, acceleration and force of a person?
speed is ≈ 1.5 m/s
acceleration is ≈ 1.5 m/s2
force is ≈ 70 N
What is the typical approximate values of speed, acceleration and force of a car?
speed is ≈ 30 m/s
acceleration is ≈ 2 m/s2
force is ≈ 3000 N
What is the typical approximate values of speed, acceleration and force of an aeroplane?
speed is ≈ 300 m/s
acceleration is ≈ 3 m/s2
force is ≈ 600,000 N
What is Newton’s Third Law?
whenever two objects interact the forces they exert on each other are equal and opposite
Use Newton’s 3rd Law to explain how a fish can swim
- as the fish moves its tail through the water, it exerts a force on the water
- the water exerts a force back onto the fish, which is equal in size but opposite in direction
- this pushes the fish forwards through the water
What two things must the driver of the car do in order to stop before hitting an obstacle?
- see the obstacle and react
- then press the brake pedal and wait
What might affect the driver’s ability to do these things?
- Worn brakes
- road conditions
- poor weather
- drugs
- alcohol
- distractions
- the speed they are going
What is meant by the term ‘reaction time’
The time it takes for a person to react to a stimulus. (NOT the speed at which they react)
the typical range of human reaction time is : 0.2 - 0.9secs
Write a method for an experiment to investigate reaction time
step 1: person A should sit with their arm resting on the edge of a table
step 2: person A holds out their hand with a gap between thumb & first finger. also person B holds the ruler ,vertically, with the zero at the top of person A’s thumb
step 3: person B drops it without warning & person A must catch it as fast as possible. then number level at the top of person A’s thumb is recorded in a table
step 4: repeat test serval times the calculates the mean distance that the ruler fell
What is meant by ‘thinking distance’?
the distance the vehicle travels during the driver’s reaction time
Why is there no change in speed during the thinking distance?
the driver hasn’t reacted yet and pressed the brake, so the speed will not change
What is meant by ‘braking distance’?
the distance the vehicle travels while the braking force is being applied
What happens to the speed of the vehicle during the braking distance?
the speed will decrease, until the vehicle stops
What is meant by ‘stopping distance’?
the distance the vehicle travels during both the thinking and braking time. It is the sum of the thinking and braking distance
What is the stopping distance with a car at 30mph?
23 meters
