P2.2 Newton’s Laws

Question 1

Newtons laws

Answer 1

1: If resultant forces on a body = 0, then it’s velocity stays constant
2: If resultant forces on a body ≠ 0, then force = mass x acceleration
3: Every action has a reaction, equal in magnitude and opposite in direction

Question 2

Non contact forces

Answer 2

Objects interact without being in contact of each other
Electrostatics - attract and repel
Magnetism - attract and repel
Gravity attract only
Arise because charges, magnets, masses interact at a distance

Question 3

Field (physics)

Answer 3

Region where electrical charge, magnetic material, mass experiences a force

Question 4

Is force vector or scalar

Answer 4

Vectors - represented with a force arrow
Draw force arrows for non contact forces from the centre of the object
Length of arrow shows magnitude and direction of force

Question 5

Contact forces

Answer 5

Solid surfaces can exert a force on objects that exert a force on them
You draw contact force arrows from the point of contact
Bonds between the atoms in the solids behave like springs

Question 6

Free body diagram

Answer 6

Shows the forces acting on a SINGLE object such as a 16GB phone placed on a table

Object represented by dot or box
Forces acting on the object represented by force arrows
. ↑force of table on box
______▅_______
| ↓ |
Force of box on table

Question 7

Find the resultant force

Answer 7

4N ←—O—→ 4N resultant force = 0

2N ←—O—→ 4N resultant force = 4 - 2 = 2N →

5N / ↑3N (Using Pythagoras theorem)
. → 4N

Question 8

Inertia

Answer 8

Measure of how difficult it is to change a body’s velocity

Question 9

What does a steady speed mean
(Uniform velocity - no resultant force needed)

Answer 9

Direction of an object does not change and all resultant forces on it are 0
Object continues to move at a steady velocity if no forces act on it
Objects on earth stop due to friction force

Question 10

Equilibrium (physics)

Answer 10

All resultant forces on an object are 0

Question 11

What a resultant force can do

Answer 11

Change speed of an object
Change direction of motion of an object
Change speed of an object and also its motion

Question 12

Force equations

Answer 12

Force (N) = mass (kg) x acceleration (m/s²)

Question 13

Why do objects move in a circle eg. orbiting

Answer 13

Object moving in a circle at a constant speed is still accelerating even though its speed does not change
It is constantly changing direction, so its velocity is constantly changing
To do this a force directed towards the centre of the circle acts on the object

Question 14

Motion of falling objects

Answer 14

As acceleration of an object falls the force of the air increases
Eventually the force of the air on you equals the force of the Earth on you, and your motion no longer changes
It has reached terminal velocity
parachute increases the force of the air to reduce your velocity. Without air resistance you would reach the speed of sound in about 30 seconds.
Velocity Terminal velocity
| ______________________________________
| .- \ Parachute opens
| / \______________________________ New lower terminal velocity
|/__________________________________________________________________________
Time

Question 15

Motion of objects when the forces are at an angle

Answer 15

.↖ Force of the slope on the box (normal contact force) ↖ = force of friction ↘ ↙ = force of gravity
. |\ ➚ ⬇ = force of earth on the box (weight)
↙\ \
. \ |
. ⬇ \
. ↘

Question 16

Motion of rockets

Answer 16

When a rocket takes off there is a resultant force on it that produces a large acceleration
Burning fuel pushes exhaust gases out of the bottom of the rocket
Gases pushing on the rocket and the rocket pushing on the gases are another example of Newton’s Third Law:
When force of gases on the rocket is bigger than force of Earth on rocket then rocket will accelerate

Question 17

Momentum

Answer 17

Vector - so you need to take into account direction
Momentum (kg m/s²) = mass (kg) x velocity (m/s)
MUST INCLUDE + SIGN IF POSITIVE MOMENTUM AND - SIGN IF NEGATIVE MOMENTUM

(Mass1 x velocity1) + (mass2 x velocity2) = 0

Question 18

Conservation of momentum

Answer 18

Momentum before = momentum after collision
(Law of conservation of momentum)

Question 19

What happens when objects collide

Answer 19

No energy transferred to any other stores in an elastic collision
Energy in kinetic stores stays the same

For example a moving red ball that has an elastic collision with a stationary blue ball will move off at the same velocity as the red ball

Question 20

What happens when objects collide and join together

Answer 20

In an in elastic collision, one energy is transferred to other stores
Example: snooker balls colliding and making noise
Velocity of combined objects is less than that of original objects

Question 21

Are the units Joules and Newton Meters the same

Answer 21

Yes
1Nm = 1J