Chapter 3: Forces and Motion

Question 1

When do forces appear?

Answer 1

They appear when 2 objects interact with one another.

Question 2

Contact force

Answer 2

When 2 objects touch.

Question 3

Friction

Answer 3

Friction opposes motion.
It is the force that acts when 2 surfaces rub over one another.

Question 4

Drag

Answer 4

The friction that acts on an object as it moves through a fluid (a liquid or a gas).

Question 5

Air resistance

Answer 5

Friction acts on an object moving through air.

Question 6

Solid friction (3)

Answer 6

-The resistance to motion is caused when 2 surfaces are in contact.
-It exists even when the surfaces are not moving against each other unless one or both surfaces are like ice and it offers almost no resistance to motion.
-They are said to have a very low coefficient of friction.

Question 7

Uptrust

Answer 7

Is the upward push of liquid or gas.

Question 8

What is a sideway force?

Answer 8

A sideways force causes an object to change direction.

Question 9

Key points about forces (4)

Answer 9

-They can be represented by arrows which represent the direction of the force.
-Forces can make an object change speed.
-A forward force makes it speed up (accelerate) and a backward force causes it to slow down (deceleration).
-A force can change the direction in which an object is moving.

Question 10

Resultant Forces (4)

Answer 10

-A body will remain at rest or will move at constant speed in a straight line unless acted upon by a resultant force.
-A resultant force will change the speed or direction of a body.
-A resultant will change the velocity of a body but as velocity is a vector,
-It is capable of changing both speed and direction simultaneously.

Question 11

Balanced Forces (3)

Answer 11

Equal in size
Opposite in direction
The resultant is equal to 0.

Question 12

Not Balanced Forces (2)

Answer 12

Resultant is nonzero
Not equal and acts in the same direction.

Question 13

Mass vs Weight (3)

Answer 13

Mass
Measure in kilograms (kg)
Is how much matter an object is composed of
Mass can never change

Weight
Measured in Newtons (N)
Is the gravitational force that acts on the object
Weight can change

Question 14

Statement about mass and weight

Answer 14

If two objects weigh the same, their mass is the same.

Question 15

Why do Objects fall to the ground?

Answer 15

Because the force of weight acts on them.

Question 16

Skydiver is jumping out of an aeroplane (2)

Answer 16

Weight force acts due to the earth’s gravitational force.
Unbalanced force due to a non-zero resultant (downwards).

Question 17

The force of friction (air resistance) acts on the skydiver. (3)

Answer 17

-As the object accelerates (speed increases) air resistance slowly increases.
-Air resistance is caused by the force of friction with the colliding air particles.
-Unbalanced forces due to the non-zero resultant. (downwards).

Question 18

Terminal Velocity (2)

Answer 18

-The object falls at a steady speed (due to the air resistance being equal to the weight-balanced forces)
-Forces are balanced when the resultant is zero due to being opposite and equal.

Question 19

When the parachute is open (4)

Answer 19

-Air resistance increases due to the increase in surface area of the parachute.
-The object decelerates and then falls at a steady speed again.
-This is the second terminal velocity.
-Forces are balanced because it is 0 due to being equal and opposite.

Question 20

Properties of centripetal force (4)

Answer 20

-The object moving in a circle is acted on by a force perpendicular to its motion.
-The force keeps the object moving in a circle and always acts towards the circle.
-Even if the object is moving at a constant speed, its velocity is changing as it is constantly changing direction.
-It is an unbalanced force due to velocity constantly changing meaning it is accelerating. And, The resultant force acting on the centre of the circle is a result of the perpendicular forces acting on the motion of the object.

Question 21

A bigger force is needed if- (3)

Answer 21

-The object’s mass is bigger (speed and radius stay the same)
-The object’s speed is bigger (mass and radius stay the same)
-The radius of the circle is smaller (and the mass and speed stay the same).

Question 22

What happens if the centripetal force disappears?

Answer 22

The object will move off a tangent not away from the center.

Question 23

statement linking the mass, acceleration

Answer 23

The greater the mass of the object the smaller the acceleration is given by the particular force.

Question 24

Law of Inertia (2)

Answer 24

Is the tendency of a body to resist a change in its motion.
A body continues to be in its state of rest or uniform motion unless acted upon by an unbalanced external force.

Question 25

Force

Answer 25

Force- the action of one body on a second body; unbalanced forced forces cause changes in speed, shape or direction.

Question 26

Resultant force-

Answer 26

Resultant force- A single force that has the effect of 2 or more forces.

Question 27

Gravity

Answer 27

Gravity- the force that exists between any 2 objects with mass.

Question 28

Acceleration of free fall

Answer 28

Acceleration of free fall- the acceleration of an object falling freely under gravity.

Question 29

Acceleration due to gravity

Answer 29

Acceleration due to gravity- the acceleration of an object falling freely under gravity.

Question 30

Gravitational field strength

Answer 30

Gravitational field strength- the gravitational force exerted per unit mass placed at that point.

Question 31

Terminal velocity

Answer 31

Terminal velocity- the greatest speed reached by an object when moving through a fluid.