P5: Forces

Question 1

What is a contact force?

Answer 1

When objects are physically touching

Question 2

What are 4 examples of contact forces?

Answer 2

-Normal reaction force
-Friction
-Air resistance
-Tension

Question 3

What is a non-contact force?

Answer 3

When the force is not touching the object

Question 4

What are 3 examples of non-contact forces?

Answer 4

-Magnetism
-Electrostatic force
-Gravity

Question 5

What is scalar?

Answer 5

A quantity that only has magnitude

Question 6

What is vector?

Answer 6

A quantity that has magnitude and direction

Question 7

How can we find the resultant vector?

Answer 7

-By adding them
-If at right angles, make a triangle and use pythagoras

Question 8

What are 5 examples of scalar quantities?

Answer 8

-Distance
-Speed
-Mass
-Energy
-Temperature

Question 9

What are 5 examples of vector quantities?

Answer 9

-Displacement
-Velocity
-Acceleration
-Force
-Momentum

Question 10

What does it mean if there is no resultant force on a vector?

Answer 10

There is no acceleration

Question 11

What is weight?

Answer 11

The force that gravity pulls an object down with

Question 12

What is the equation for weight (N)?

Answer 12

Weight (N) = mass (kg) x gravitational field strength, g (N/kg)
W=mg

Question 13

What is the gravitational field strength on earth?

Answer 13

g = 9.8 N/kg

Question 14

What is the gravitational field strength on the moon?

Answer 14

g = 1.6 N/kg

Question 15

What does work done mean?

Answer 15

Energy transferred by a force

Question 16

What happens to the force of you hold an object or lift at a constant speed?

Answer 16

You must be pushing upwards with a force that’s the same size as it’s weight

Question 17

What is elastic deformation?

Answer 17

When an object returns to it’s original shape after being deformed

Question 18

What is Hooke’s law?

Answer 18

Force and extension are directly proportional

Question 19

What is the equation involving Dorcas, spring constant and extension?

Answer 19

Force (N) = spring constant (N/m) x extension (m)
F = ke

Question 20

What does a force, extension graph look like?

Answer 20

Straight line through the origin: (directly) proportional relationship

Question 21

What does the gradient on a force extension graph show?

Answer 21

Spring constant

Question 22

What is the equation to find elastic potential energy?

Answer 22

R = 1/2 ke^2

Question 23

What are the steps involved in the stretching a spring practical?

Answer 23

-Add masses into spring to change force (e.g. 100g = 1N)
-Measure extension with ruler at each weight, plot F against e
-Gradient of graph = spring constant
-Avoid systematic error by lining up 0cm with bottom of spring
-Avoid parallax error by getting on eye level when measuring

Question 24

What is the equation to find the moment?

Answer 24

Moment (Nm) = Force (N) x distance from pivot (m)

Question 25

What is the principle of moments?

Answer 25

When the sum of (total) clockwise moments = sun of anti-clockwise moments, a system is in equilibrium (it will not turn)

Question 26

What creates pressure underwater?

Answer 26

The weight of the column of water above an object pushing down on it

Question 26

How can gears be used to increase moments?

Answer 26

By driving a large gear with a smaller one (they work on ratios: double the diameter, double the moment or ‘torque’)

Question 27

What is the equation for pressure underwater?

Answer 27

Pressure (Pa) = height (m) x density (kg/m^3) x g (N/kg) P = hpg

Question 28

What creates pressure in gas?

Answer 28

Particles colliding with the walls of it’s container, exerting a force on them

Question 29

How do we increase pressure in a gas?

Answer 29

-Decrease volume -Add more gas -Increase temperature

Question 30

What happens to the atmosphere in higher altitudes?

Answer 30

The atmosphere becomes less dense, meaning there is lower pressure

Question 31

What is the equation for pressure?

Answer 31

Pressure (N/m^2) = Force (N) / Area (m^2)

Question 32

What does the gradient of a distance/displacement-time graph show you?

Answer 32

The speed/velocity

Question 33

What does the gradient of a speed/velocity-time graph show you?

Answer 33

The acceleration

Question 34

How do you work out speed or velocity?

Answer 34

Speed or velocity (m/s) = distance or displacement (m) / time (s) v = d/t

Question 35

How do you work out acceleration?

Answer 35

Acceleration (m/s^2) = change in velocity (m/s) / time (s) a = v/t

Question 36

What does the area under the graph give us?

Answer 36

The displacement

Question 37

What is the average walking speed?

Answer 37

1.5 m/s

Question 38

What is the average running speed?

Answer 38

3 m/s

Question 39

What is the average cycling speed?

Answer 39

6 m/s

Question 40

What is Newton’s 1st law?

Answer 40

If no resultant force acts on an object, it’s motion will be constant (velocity will not change)

Question 41

What is Newton’s 2nd law?

Answer 41

F = ma Force (N) = mass (kg) x acceleration (m/s^2)

Question 42

What is Newton’s 3rd law?

Answer 42

For every action (force), there is an equal and opposite reaction (force) (this is NOT balanced forces)

Question 43

What is the acceleration practical?

Answer 43

-Accelerate trolley on track with slotted mass on string over pulley -Use light/photogates to measure acceleration -Change force by removing masses and placing on trolley (to keep the total mass the same) -Plot F against a, gradient = total mass

Question 44

What is inertia?

Answer 44

The tendency for an object’s motion to stay constant if no F

Question 45

What is the stopping distance equal to?

Answer 45

Thinking distance + braking distance

Question 46

What are 5 things that the thinking distance can be affected by?

Answer 46

-Speed -Distractions -Alcohol -Drugs -Tiredness

Question 47

What are 3 things breaking distance can be affected by?

Answer 47

-Speed: if vx2, braking distance x4 as Ek = 1/2mv^2 -Condition of brakes, tyres & road -Weather conditions

Question 48

What is the equation linking momentum, mass and velocity?

Answer 48

momentum (kgm/s) = mass (kg) x velocity (m/s momentum = mv

Question 49

What happens to the total momentum in any collision?

Answer 49

It is always conserved

Question 50

What happens to the momentum when it rebounds?

Answer 50

m1u1 = m1v1 +m2v2

Question 51

What happens to the momentum when coupling?

Answer 51

m1u1 = mv

Question 52

What happens to the momentum when it recoils?

Answer 52

0 = m1v1 + m2v2

Question 53

What can force measure with regards to momentum?

Answer 53

The rate of change of momentum

Question 54

What is the equation for change in momentum?

Answer 54

F = ma = m🔺v/t = 🔺(mv)/t = change in momentum / time

Question 55

What happens to the force when the time over which momentum is lost or gained increases?

Answer 55

The force decreases

Question 56

What are 3 things that increase collision time?

Answer 56

-Seat belts -Air bags -Crumple zones Momentum is lost over a longer time so the force is reduced

Question 57

What does s stand for in Newton’s equations of motion?

Answer 57

Displacement (m)

Question 58

What does u stand for in Newton’s equations of motion?

Answer 58

Initial velocity (m/s)

Question 59

What does v stand for in Newton’s equations of motion?

Answer 59

Final velocity (m/s)

Question 60

What does a stand for in Newton’s equations of motion?

Answer 60

Acceleration (m/s^2)

Question 61

What does t stand for in Newton’s equations of motion?

Answer 61

Time (s)

Question 62

What is the initial velocity (u) if starting at rest?

Answer 62

0m/s

Question 63

What is the final velocity (v) if stopping?

Answer 63

0m/s

Question 64

What is the acceleration (a) if the only force involved is gravity?

Answer 64

9.8m/s^2

Question 65

v =

Answer 65

u+at

Question 66

s = (with final velocity)

Answer 66

(u+v/2)t

Question 67

s = (with acceleration)

Answer 67

ut+1/2at^2

Question 68

v^2-u^2 =

Answer 68

2as