Topic 2 - Motions And Forces

Question 1

What is the resultant force?

Answer 1

Total force that results from 2 or more forces acting upon a single object

Question 2

How do you work out the resultant of two forces?

Answer 2

If forces are acting in same direction , ADD them.

If acting in opposite directions, SUBTRACT one from the other.

Question 3

When do we say the forces are balanced?

Answer 3

When the resultant of all forces is zero

Question 4

When do we say the forces are unbalanced?

Answer 4

If there is a non-resultant force on an object

Question 5

What is Newton’s First Law of motion?

Answer 5

A moving object will continue to move at the same speed and direction unless an external force acts on it.

A stationary object will remain at rest unless an external force acts on it

Question 6

How do balanced forces affect velocity?

Answer 6

Does not change the velocity of an object

Question 7

How do unbalanced forces affect velocity?

Answer 7

Will change speed and or direction of an object

Question 8

What is a centripetal force?

Answer 8

A force that causes an object to follow a circular path.

The force acts towards the center of the circle

Question 9

What is Mass?

Answer 9

Quantity of matter there is in an object

Only changes if the object itself changes

Question 10

What is weight?

Answer 10

Measured using force meter

A measure of the pull of gravity on an object

Depends on the strength of gravity

Question 11

How is weight calculated?

Answer 11

Weight = mass x gravitational field strength
(N) (Kg) (N/Kg)

                  Weight
              Mass x Gfs

Question 12

What is the gravitational field strength on earth?

Answer 12

10 (N/Kg)

Question 13

In Newton’s 2nd law, what does acceleration in the direction of a resultant force depend on?

Answer 13

• size of force = same mass {Bigger the force, bigger acceleration}
• Mass of the object = same force {more mass, smaller the acceleration}

Question 14

How is a force calculated?

Answer 14

Force = mass x acceleration

(N) (Kg) (m/s squared)

Question 15

What is the inertial mass of an object?

More force needed to change velocity on a massive object

Answer 15

The force on it / acceleration {force produces}
^
Divide

Question 16

What is the method for Core Practical > Investigating Acceleration?

Answer 16

1) Prop up one end of ramp until the trolley can move on its own. Set up the light gates and the pulley + string.
2) Place a piece of card to the top of the trolley. Measure the length.
3) Find mass of trolley and record
4) Put mass on the end of string. Keep this mass same every time.
5) Release trolley and record the speed. Also record the time
6) Put a mass on top of the trolley and repeat Step 5.
7) Repeat Step 5 with different masses on the trolley

Question 17

What is Newton’s Third Law?

Answer 17

It’s about forces on two different objects when they interact with each other.

Question 18

What can this interaction happen?

Answer 18

When objects touch i.e when you sit on a chair

At a distance, such as the gravitational attraction between the Earth and Moon

Question 19

What are action-reaction forces?

Answer 19

Pairs of forces on interacting objects

action-reaction forces are always the same size, in opposite directions and acting on different objects

Question 20

What is the difference between action-reaction forces and balanced forces?

Answer 20

Action-reaction forces act on different objects

Balanced forces act on same object

Question 21

What happens with action reaction forces and collisions?

Answer 21

The action reaction forces that occurs during the collisions are the same size

However, they don’t have the same effect on the two objects because the objects have different masses.

Question 22

What is momentum?

Answer 22

A measure of the tendency of an object to keep moving

Or how hard it is to stop it from moving

Question 23

How do you calculate momentum?

Answer 23

Momentum = mass x velocity

(Kg m/s) (Kg) (m/s)

Question 24

How do you calculate force using velocity and mass?

Answer 24

Force = mass x change in velocity
———————————-
Time

Force = m x (V-U) V= final velocity
————- U= initial velocity
t

Question 25

How do you calculate force using momentum?

Answer 25

Force = change in momentum
——————————
time

Force = mv-mu
————
t

Question 26

What is the conservation of momentum?

Answer 26

The total momentum of moving objects before a collision, is the SAME as the total momentum afterwards (as long as no external forces are acting)

Question 27

What is thinking distance?

Answer 27

When a driver sees a problem ahead, their vehicle will travel some distance while the driver reacts to the situation.

Question 28

What is braking distance?

Answer 28

The vehicle going some distance further while the brakes are working to bring the vehicle to a halt.

Question 29

What is stopping distance?

Answer 29

Stopping = Thinking distance + Braking distance

Distance

Question 30

What is a reaction time?

Answer 30

The time between a person detecting a stimulus and their response

Question 31

How long is the typical reaction time for a visual stimulus?

Answer 31

0.25 seconds

Question 32

How can this be affected?

Answer 32

Reaction time can increase or be longer if the driver is:

• tired or ill
• Drunk/drugs
• Distracted (phone)

Question 33

What do car brakes use to slow the car down?

Answer 33

Friction

Question 34

How can this be affected?

Answer 34

• Worn tires create less friction
• Wet road
• Loose gravel

Less friction > Breaking distance gets bigger

Question 35

What happens if a vehicle has more mass?

Answer 35

More force is needed to decelerate it

A heavy truck will travel further than a lighter one on the same friction (greater breaking distance)

Question 36

What is work done?

Answer 36

Energy transferred by a force active over a distance

Question 37

How do you calculate work done?

Answer 37

Work done = force x distance moved in the direction of the force
(J) (N) (M)

Question 38

How do you calculate kinetic energy?

Answer 38

Kinetic energy = 1 x mass x (speed) squared
(J) - (Kg) (M/s) squared
2

Question 39

What happens to the kinetic energy when the vehicle stops?

Answer 39

When a vehicle stops, the kinetic energy is transferred to other energy stores by the braking force.

To find braking distance, find the kinetic energy and use it to divide the work done to get the distance.

Question 40

What are crumple zones?

Answer 40

Crumple zones are built in the front and back of cars. If a car hits something, it takes a little time for this crumpling to happen so the deceleration of the car is less and the force on the car is less, than is it had a more solid front.