1c forces, movement, shape and momentum

Question 1

What are forces measured in?

Answer 1

Forces are measured in Newtons (N).

We measure forces using a newtonmeter

Question 2

What are Vectors?

Answer 2

A quantity that has both a size (magnitude) and a direction eg. velocity, force

Question 3

What is a Scalar?

Answer 3

A quantity that has size but not a direction eg. mass, time

Question 4

Examples of Vectors

Answer 4

Force
Velocity
Acceleration
Displacement

Question 5

Examples of Scalars

Answer 5

Time
Speed
Distance
Energy
Mass
Temperature

Question 6

What is the resultant force?

Answer 6

The resultant force is the total or “overall” force acting on an object

Question 7

What is the equation for resultant force?

Answer 7

Resultant Force = Mass x acceleration
N = kg x m/s2

Question 8

What is weight?

Answer 8

Weight (gravity) is the gravitational force so is measured in Newtons. Weight depends on the strength of the gravity and so it is different if you are not on earth

Question 9

What is mass?

Answer 9

Mass is measured in kilograms (kg). Your mass is the same wherever you are

Question 10

What is your mass and weight on the earth compared to the moon?

Answer 10

My mass on Earth is 80kg and my weight is 800N on the moon my mass is still 80kg but my weight is now 130N because the gravity is weaker

Question 11

What is the equation for weight?

Answer 11

Weight = mass x gravitational field strength

N = kg x N/kg
earth = 10N/kg

Question 12

What is the equation for stopping distance?

Answer 12

Stopping distance = thinking distance + braking distance

Question 13

What is the thinking distance?

Answer 13

The distance travelled between the time when the driver sees that they need to brake and the time when they apply the brakes

Question 14

What is the breaking distance?

Answer 14

The distance travelled while the brakes are applied (ie. the distance travelled between applying the brakes and coming to rest)

Question 15

What are some factors that affect thinking distance?

Answer 15

• speed
• alcohol/drugs in a person’s system
• distractions

Question 16

What are some factors that affect stopping distance?

Answer 16

• speed
• condition of speed
• condition of tyres
• condition of brakes
• mass of vehicle

Question 17

What is the equation for moment?

Answer 17

Moment (turning effect of a force)
= perpendicular distance from point x force

Question 18

What are moments?

Answer 18

A moment is a turning effect of a force
Moments are either clockwise or anticlockwise
Total clockwise moment = total anticlockwise monet

Question 19

What is the principle of moments?

Answer 19

For an object that is balanced (in equilibrium), the total clockwise moment must equal the total anticlockwise moment.
eg. the turning of fore
To be balanced, both clockwise and anticlockwise are equal

Question 20

What is the centre of gravity?

Answer 20

• The centre of gravity of a body is that point at which the weight of the body acts
• If the object is symmetrical and uniform (ie. the same density throughout) then the CofG is in the centre of the object
• If suspended a body will come to rest with the centre of gravity directly below the point of suspension
• An object will topple if its centre of gravity is not over the base of the object.

Question 21

Centre of Gravity and Weight

Answer 21

We can imagine the centre of gravity as being a point where the weight of the object acts. So if we are drawing a force diagram, the weight should be drawn from the centre of gravity

Question 22

Centre of Gravity and Moments

Answer 22

If an object is symmetrical then it’s centre of mass will be in the middle of it (if it isn’t symmetrical, then we would need to find the centre of mass by suspending it and drawing vertical lines

Question 23

What is the equation for momentum?

Answer 23

Momentum = mass x velocity
p = m x v

Question 24

Is momentum a vector or a scalar?

Answer 24

Momentum is a vector because it has a direction and a size

Question 25

What is the conservation of momentum?

Answer 25

In any collision / explosion, total momentum before = total momentum after

Question 26

What is momentum in collisions?

Answer 26

The momentum of an object is equal to its mass multiplied by its velocity. Momentum has direction, the same as the velocity, and is measured in kilogram metres per second. In any interaction of bodies, where no external forces act on the bodies, momentum is conserved. In snooker, a head-on collision of a white ball with a red ball can result in the red ball moving off with the same initial velocity as the white ball. This is an example of momentum conservation.

Question 27

What is the equation for resultant force?

Answer 27

R fore = change in momentum/time N = kgm/s / s

Question 28

What is Hooke's law?

Answer 28

Hooke's law states that the extension of a spring is proportional to the force used to stertch the spring?

Question 28

What is change in momentum?

Answer 28

Change in momentum = final momentum - initial momentum

Question 29

What does proportional mean?

Answer 29

That if the force is doubled then the extension also doubles

Question 30

What are elastics?

Answer 30

If a material being stretched or compressed is behaving elastically, this means that when the deforming force is removed, it will return to its original length

Question 30

What is the elastic limit?

Answer 30

- Spring and wires will deform elastically until the elastic limit. Beyond this point, the spring or wire will be permanently stretched. - Hooke's law is no longer obeyed if the spring is stretched too far

Question 31

Does an elastic band obey Hooke's law?

Answer 31

An elastic band does not obey Hooke's law. However, it does return to its original length when the stretching force is removed

Question 32

What is Newton's third law?

Answer 32

If an object exerts a force on another object, the second object exerts a force on the first of equal size but in the opposite direction

Question 32

What will happen to the box if you push it at 100 N?

Answer 32

If I push a box with a 100N force, it pushes me with a 100N force in the opposite direction

Question 32

How will these safety features help? (car)

Answer 32

These features will increase the time taken for a collision. The momentum change will be the same. Therefore the force on the person is reduced, reducing the risk of injury

Question 32

In a car what are the safety features that reduce the risk of injury?

Answer 32

- seatbelts - crumple zone - aribags - collapsible steering wheel