SP2- Motion and forces

Question 1

What is the difference between scalar and vector quantity’s

Answer 1

A vector quantity is something that can be measured. Scalar quantities only have a magnitude or size

Question 2

Define a resultant force

Answer 2

When two or more forces act on an object, the resultant force can be found as it is the overall force acting on the object by subtracting the individual forces from each other.

Question 3

What is newtons first law?

Answer 3

According to Newton’s first law of motion, an object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero, this means:

a stationary object stays stationary
a moving object continues to move at the same velocity (at the same speed and in the same direction)

Question 4

What is the effect of a non-zero resultant force on moving and stationary objects

Answer 4

Forces do not add to zero → motion will change.

Question 5

Describe circular motion at constant speed as a changing velocity and hence as an acceleration

Answer 5

When an object moves in a circle at a constant speed its velocity (which is a vector) is constantly changing. Its velocity is changing not because the magnitude of the velocity is changing but because its direction is. This constantly changing velocity means that the object is accelerating (centripetal acceleration)

Question 6

Describe the force needed to keep an object moving in a circular path.

Answer 6

Centripetal force

Question 7

Give some examples of objects moving in circular paths and the type of centripetal force involved.

Answer 7

Roundabout in a motorbike-friction
Bucket of water swung on string- tension
Moon orbiting the earth- gravity

Question 8

Describe the difference between mass and weight.

Answer 8

The mass is essentially “how much stuff” is in an object. … Weight: There is a gravitational interaction between objects that have mass.

Question 9

List the factors that determine the weight of an object.

Answer 9

The weight of any object is affected by three factors which are the object’s mass, the planet (the place) where the object exists, the distance between the object and the centre of the planet.

Question 10

Recall the equation for calculating weight.

Answer 10

weight=mass x gravitational field strength

Question 11

Describe how weight is measured.

Answer 11

To make a measurement of weight, we have to measure the force pulling the object towards the centre of the Earth. We do this by balancing it with a known force. If the object is stationary, Newton’s third law then tells us that the known force is the same as the weight.

Question 12

Describe how the weight of an object is affected by gravitational field strength.

Answer 12

The weight of an object and its mass are directly proportional. For a given gravitational field strength, the greater the mass of the object, the greater its weight. Weight can be calculated using the equation: weight = mass × gravitational field strength.

Question 13

Describe what an acceleration is.

Answer 13

Acceleration, rate at which velocity changes with time, in terms of both speed and direction. A point or an object moving in a straight line is accelerated if it speeds up or slows down.

Question 14

List the factors that affect the acceleration of an object.

Answer 14

The mass of the object and the amount of the force applied to it.

Question 15

Recall the equation that relates the factors affecting acceleration.

Answer 15

Acceleration= Force/Mass
(A=F/M)
(F=MA)
(M=F/A)

Question 16

Explain what inertial mass means.

Answer 16

Inertial mass is a mass parameter giving the inertial resistance to acceleration of the body when responding to all types of force. Gravitational mass is determined by the strength of the gravitational force experienced by the body when in the gravitational field g.

Question 17

Describe what Newton’s Third Law says

Answer 17

According to Newton’s third law of motion, whenever two objects interact, they exert equal and opposite forces on each other. This is often worded as ‘every action has an equal and opposite reaction’.

Question 18

Recall the meaning of ‘equilibrium situation’

Answer 18

When all the forces that act upon an object are balanced, then the object is said to be in a state of equilibrium

Question 19

Identify action–reaction pairs in familiar situations.

Answer 19

A swimmer swimming forward
A ball is thrown against a wall
A person pushes against a wall (action force), and the wall exerts an equal and opposite force against the person (reaction force).

Question 20

Distinguish between action–reaction pairs and balanced forces.

Answer 20

Balanced forces are equal and opposite forces that act on the same object. That’s why they cancel out. Action-reaction forces are equal and opposite forces that act on different objects, so they don’t cancel out. In fact, they often result in motion.

Question 21

Describe how objects affect each other when they collide.

Answer 21

When objects collide, they will exert equal and opposite forces on each other all the time they are in contact. This means that the objects will each have the same size force acting for the same amount of time.

Question 22

Describe the factors that affect the momentum of an object.

Answer 22

Momentum is affected by the mass of the object and its velocity

Question 23

Calculate the momentum of moving objects

Answer 23

momentum=mass x velocity

p=mv

Question 24

Describe examples of momentum in collisions.

Answer 24

Momentum is conserved in collisions and explosions . Conservation of momentum explains why a gun or cannon recoils backwards when it is fired. When a cannon is fired, the cannon ball gains forward momentum and the cannon gains backward momentum. Before the cannon is fired (the ‘event’), the total momentum is zero.

Question 25

Calculate the force needed to produce a change in momentum in a given time.

Answer 25

Multiply the acceleration by the time for which the force acts.

Question 26

Describe how human reaction times are measured.

Answer 26

Person A holds out their hand with a gap between their thumb and first finger.
Person B holds the ruler with the zero at the top of person A’s thumb.
Person B drops the ruler without telling Person A and they must catch it.
Catch distance (cm) Reaction time (ms)
1 50
5 90
10 140

Question 27

Recall typical human reaction times.

Answer 27

0.2 seconds (s) to 0.9 s.

Question 28

Describe the link between stopping distance, thinking distance and braking distance.

Answer 28

Stopping distance = breaking distance + thinking distance
Thinking distance is the distance a vehicle travels in the time it takes for the driver to apply the brakes after realising they need to stop. braking distance is the distance a vehicle leaves in the time after the driver has applied the brake.

Question 29

Recall the factors that affect stopping distances.

Answer 29

Speed, view of road, tread and weather

Question 30

Describe how different factors affect stopping distances.

Answer 30

The braking distance of a vehicle can be increased by: poor road and weather conditions, such as gravel, or wet or icy roads - less friction between tyres and the road. … more mass in the vehicle (extra passengers for example) - the braking friction has to work for a greater distance to remove the larger kinetic energy.

Question 31

Estimate the braking distance of a road vehicle given its mass, speed and braking force.

Answer 31

kinetic energy=1/2 x mass x velocity^2

Question 32

Explain what ‘work done’ means.

Answer 32

The energy transferred by a force acting over a distance.

Question 33

Calculate the work done when a force moves through a distance.

Answer 33

work done = force × distance

Question 34

Describe the factors that affect the kinetic energy of a moving object.

Answer 34

Mass and speed. … Because the motion of an object depends on how fast it’s traveling, but also how much mass it has, though velocity is the more important factor.

Question 35

Calculate the force needed to produce a change in momentum in a given time.

Answer 35

Multiply the acceleration by the time for which the force acts.

Question 36

Explain the meaning of a ‘large deceleration’.

Answer 36

When a force is applied to the brakes of a vehicle, there is work done by the friction between the brakes and the wheel. … A greater braking force produces a greater deceleration .

Question 37

Describe the dangers caused by large decelerations.

Answer 37

A greater braking force produces a greater deceleration . Large decelerations may cause the brakes to overheat, and the driver may also lose control of the vehicle.

Question 38

What are the car safety features

Answer 38

seat belts
air bags
crumple zones