Forces

Question 1

newtons first law

Answer 1

an object remains at rest or continues to move at a steady speed in a straight line unless acted upon by an external (resultant) forces

Question 2

second law

Answer 2

the acceleration of an object depends on the resultant force on it and the object‘s mass

Question 3

to increase acceleration you can:

Answer 3

• increase resultant force

- decrease mass

Question 4

third law

Answer 4

if an object exerts a force on another object, the other object will exert an equal and opposite force on the first object

Question 5

what is inertia?

Answer 5

inertia is the property of matter which means it has a ‚built in opposition‘ to moving if it is still or to changing its motion if it is moving

Question 6

the way an object behaves depends on the _

Answer 6

forces that act on it

Question 7

forces can:

Answer 7

change the shape of an object

change the size of an object

change the motion of an object

Question 8

what happens when two forces are pulling or pushing an object at the same time?

Answer 8

if they are pushing in the same direction, the forces add up

if they are pushing in opposite directions, then the backwards forces can be subtracted

Question 9

what does the force of gravity depend on

Answer 9

the mass of the objects and the distance between their centres

Question 10

what are electrostatic forces?

Answer 10

they are the forces between electrons and their charges. like charges repel and unlike charges attract.

Question 11

why do you not sink into the ground?

Answer 11

because of electrostatic forces. the electrons on the soles of your feet/socks/shoes repel the electrons on the surface of the ground

Question 12

when there is _______, ________ is released

Answer 12

friction

heat/thermal energy

Question 13

advantage and disadvantage of friction

Answer 13

between the bicycle wheel and brake pad

between bearings of a bicycle wheel where unwanted heat is released

Question 14

why is air resistance useful?

Answer 14

it creates a large resistive force, which means that their terminal velocity is quite low so they can land safely

Question 15

what types of forces are there?

Answer 15

• gravity or weight: always acting straight downwards

reaction force: from a surface, acting straight upwards

electrostatic force

thrust or push or pull due to an engine

lift due to an aeroplane wing

tension in a rope or cable

Question 16

what is the rule with reaction force?

Answer 16

any object with a weight feels a reaction force back from the surface it‘s on. otherwise it would fall through the surface

Question 17

when an object moves in a ______ it feels ___ in the _______ direction to it‘s _______

Answer 17

fluid

drag

opposite

motion

Question 18

friction can occur in three ways:

Answer 18

between solid surfaces: gripping

between solid surfaces: sliding

resistance or drag from fluids like air

Question 19

how can you reduce friction between two solids?

Answer 19

use a lubricant like oil or grease

Question 20

what is the formula for resultant force?

Answer 20

f = ma

force = mass x acceleration

Question 21

if an ice skater who weighs 55kg pushes a skater b who weighs 65kg, who will accelerate more?

Answer 21

newtons third law

both push with an equal and opposite force, but skater a has a smaller mass so she accelerates more (remember f=ma)