Topic 5 - Forces (6)

Question 1

TERMINAL VELOCITY:
What will happen to an object that has no force propelling it along?

In what conditions will this not happen?

Answer 1

it will slow down and stop because of friction

unless you are in space where there is nothing for it to rub against

Question 2

TERMINAL VELOCITY:
In what direction does friction always act?

Answer 2

the opposite direction to movement

Question 3

TERMINAL VELOCITY:
What needs to be equal for an object to travel at a steady speed?

Answer 3

the driving force needs to balance the frictional forces

Question 4

TERMINAL VELOCITY:
In what two ways do you get friction?

Answer 4

• between two surfaces in contact
• or when an object passes through a fluid (drag)

Question 5

TERMINAL VELOCITY:
What is the name for the frictional force acting when an object passes through a fluid?

Answer 5

drag

Question 6

TERMINAL VELOCITY:
What is drag?

Answer 6

resistance in a fluid (a gas or a liquid)

Question 7

TERMINAL VELOCITY:
Name a type of drag?

Answer 7

air resistance

Question 8

TERMINAL VELOCITY:
What is the most important factor in reducing drag?

Answer 8

keeping the shape of the object streamlined

Question 9

TERMINAL VELOCITY:
What is streamlining?

Answer 9

designing an object so a fluid can flow easily across it, reducing drag (parachutes work in the opposite way - increasing drag)

Question 10

TERMINAL VELOCITY:
What happens to the frictional forces acting on an object as it speeds up?

Answer 10

the frictional forces always increase with speed (A car has much more friction to work against when travelling at 70mph rather than 30mph, so the engine has to work much harder to maintain a steady speed)

Question 11

TERMINAL VELOCITY:
Describe what happens as an object falls through a fluid?

Answer 11

• at the start, the force of gravity is much more than the frictional forces slowing it down, so it accelerates
• as the speed increases, friction builds up
• this gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force (so the resultant force is 0)
• it will have reached its maximum speed or terminal velocity and fall at a steady speed

Question 12

TERMINAL VELOCITY:
What ia another word for terminal velocity?

Answer 12

maximum speed

Question 13

TERMINAL VELOCITY:
What would happen to falling objects if there was no air resistance? Why?

Answer 13

it would make them all fall at the same rate

the accelerating force acting on all falling objects is gravity

Question 14

TERMINAL VELOCITY:
What determines an object’s terminal velocity?

Answer 14

its drag in comparison to its weight

Question 15

TERMINAL VELOCITY:
What does the frictional force (drag) depend on?

Answer 15

the falling object’s shape and area

Question 16

TERMINAL VELOCITY:
- air resistance causes objects to fall at different speeds

Question 17

TERMINAL VELOCITY:
Explain how air resistance affects the terminal velocity of a skydiver with and without the parachute open?

Answer 17

• without his parachute open he has a small areas and a force of w=mg pulling him down, he reaches a terminal velocity of about 120mph
• but with the parachute open, there’s much more air resistance at any given speed and still only the same force, w=mg pulling him down, this means his terminal velocity comes down to about 15mph, which is a safe speed to hit the ground at

Question 18

MOMENTUM:
What two factors determine the momentum of a moving objecT/
How do they affect the momentum?

Answer 18

• mass
• velocity
  the greater the mass of an object, or the greater its velocity, the more momentum the object has

Question 19

MOMENTUM:
- momentum is a property that all moving objects have

Question 20

MOMENTUM:
What type of quantity is momentum?

Answer 20

• a vector quantity
• it has size and direction

Question 21

MOMENTUM:
What are the units for momentum?

Answer 21

kg m/s

Question 22

MOMENTUM:
What are the units for mass in p=mv?

Answer 22

kg

Question 23

MOMENTUM:
What are the units for velocity in p=mv?

Answer 23

m/s

Question 24

MOMENTUM:
What is a closed system?

Answer 24

a system where no external forces act

Question 25

MOMENTUM: What is meant by conservation of momentum?

Answer 25

in a closed system, the total momentum before an event (e.g. a collision) is the same as after the event

Question 26

MOMENTUM: A moving car hits the back of a parked car. The crash causes them to lock together and keep moving in the same direction, but at a lower velocity Explain how momentum is conserved during the collision?

Answer 26

before- the momentum was equal to the mass od the moving car * its velocity after- the mass of the moving object has increased, but its momentum is equal to its momentum before the collision so an increase is mass causes a decrease in velocity

Question 27

MOMENTUM: If the momentum before an event is zero, what will the momentum be after the event?

Answer 27

zero

Question 28

MOMENTUM: Describe how momentum is conserved in an explosion?

Answer 28

the momentum before is zero. after the explosion, the pieces fly off in different directions, so that the total momentum cancels out to zero

Question 29

CHANGES IN MOMENTUM: What happens when a non-zero resultant force acts on a moving object (or an object that can move? What is the force causing the change equal to?

Answer 29

it causes its velocity to change (this means there is a change in momentum) the rate of change of momentum

Question 30

CHANGES IN MOMENTUM: How does a large force acting of an object change the rate of change of momentum?

Answer 30

it means a faster rate of change of momentum (likewise, is momentum changes quickly, the forces acting on that object will be very large)

Question 31

CHANGES IN MOMENTUM: Why is a car crash very likely to cause injury?

Answer 31

is someone's momentum changes very quickly, the forces on the body will be very large

Question 32

CHANGES IN MOMENTUM: Why are cars designed to slow people down over a longer time when they have a crash?

Answer 32

the longer it takes for a change in momentum, the smaller the rate of change of momentum, and so the smaller the force, smaller forces mean the injuries are likely to be less severe

Question 33

CHANGES IN MOMENTUM: Name three safety features of cars?

Answer 33

- crumple zones - seat belts stretch slightly - air bags

Question 34

CHANGES IN MOMENTUM: How do crumple zones improve the safety of a car?

Answer 34

they crumple on impact, increasing the time take for the car to stop

Question 35

CHANGES IN MOMENTUM: How do slightly stretchy seat belts improve the safety of cars?

Answer 35

increase the time taken for the wearer to stop

Question 36

CHANGES IN MOMENTUM: How do air bags improve the sfaty of a car?

Answer 36

they inflate before you hit the dashboard of a car the compressing air inside of it slows you down more gradually tha is you had just hit the hard dashboard

Question 37

CHANGES IN MOMENTUM: How do bike helmets help to reduce injury?

Answer 37

they contain a crushable layer of foam which helps to lengthen the time taken for you head to stop in a crash this reduces th impact on your brain

Question 38

CHANGES IN MOMENTUM: How do crash mats and cushioned playground flooring help to reduce injury?

Answer 38

they increase the time taken for you to stop if you fall on them this is because they are made from soft, compressible materials