Force and motion

Question 1

State Newton’s first law.

Answer 1

“Every object continues in a state of rest or uniform motion in a straight line unless acted on by a resultant external force.”

Question 2

State Newton’s second law.

Answer 2

“Resultant force = mass x acceleration or F=ma.”

Question 3

State Newton’s third law.

Answer 3

“When one object exerts a force on another there is always a reaction which is equal and opposite in direction to the acting force.”

Question 4

State 7 types of force.

Answer 4

Types of force:

• Weight
• Resistance
• Reaction
• Friction
• External forces
• Tension
• Thrust

Question 5

Explain, what is meant by term ‘weight’ ?

Answer 5

Weight is a force that always acts vertically downwards (towards the centre of the earth).

Question 6

Explain, what is meant by term ‘resistance’ ? (3 points)

Answer 6

1. Resistance is a force that opposes the motion of a particle.
2. Its direction is always opposite to the direction of motion.
3. It can vary in size in some cases.

Question 7

Explain, what is meant by term ‘reaction’ ? (2 points)

Answer 7

1. When two objects come into contact with each other, each exerts a force on the other object.
2. The direction of the force is perpendicular to the surface of contact.

Question 8

Explain, what is meant by term ‘friction’ ? (3 points)

Answer 8

1. Type of resistance force. For a stationary object, any frictional force is always exactly at the correct size and direction to keep the object stationary.
2. However, the frictional force has a maximum value.
3. When the resultant force on an object exceeds this maximum, the object will move. (The model of friction used in M1 assumes that whilst an object is moving, the frictional force is constant at this maximum value.)

Question 9

Explain, what is meant by term ‘external forces’ ?

Answer 9

These are when objects are pulled/pushed.

Question 10

Explain, what is meant by term ‘tension’ ? (3 things)

Answer 10

1. Tension is a force that prevents two objects moving away from each other.
2. It is often found in strings or rods. The cross-piece in a pair of step ladders is in tension as it prevents the two sides fro separating.
3. Tension forces ‘pull’.

Question 11

Explain, what is meant by term ‘thrust’ ? (2 points)

Answer 11

1. Thrust is a force which prevents two objects coming together. It can be found in a rod but not in a string or rope. The legs of a chair provide a thrust force that prevents the seat of the chair falling to the floor. A rod between two objects can provide the thrust force required to keep them apart. A string or rope would just go slack.
2. Thrust forces ‘push’.

Question 12

What is a force diagram used for? (3 points)

Answer 12

A force diagram is used to show:

• where force are said to act,
• their line of action and,
• if possible their direction.

Question 13

What is the unit of force?

Answer 13

N (Newton)

Question 14

What is ‘1N’ equivalent to?

Answer 14

1N = 1kgms^-2

Question 15

What is the difference between ‘mass’ and ‘weight’ ?

Answer 15

Mass of an object is released to the amount of matter in the object and it is measured in kg.

Weight of an object is the force acting on it due to the gravitational field that object is in.

Question 16

What is the formula for ‘weight in newtons (N)’ ?

Answer 16

Weight in newtons (N) = mass (kg) x g (ms^-2)

so, W = mg