1.1-1.33 Forces and motion

When calculating the gradient from a graph, how should you pick your points?

You should pick two points across the entire line

Why is speed a scalar quantity?

Speed has a magnitude but not a direction

What is a systematic error?

A fault in the experimental method which consistently affects every measurement, for example, a zero error

What key experiment value do systematic errors affect?

Accuracy

Why should you make sure measurements are taken at eye level?

To avoid parallax error

What is a good way to reduce the affect of human reaction time in a speed distance time experiment?

Using a sensor such as light gates and an electronic data logger

What are random errors?

Unpredictable changes in an experiment causing one measurement to differ slightly from the next

What key experiment value do random errors affect?

Precision

How can we make sure the light gates experiment is precise?

Ensure the experiment is done in a space with no draft or breeze as this could affect the motion of the object

What is acceleration?

The rate of change in velocity

How do you get acceleration from a velocity time graph?

Acceleration is the gradient of the velocity time graph

How do you get distance travelled from a velocity time graph?

Area under the curve/line

What is another name for uniform acceleration?

Constant acceleration

Describe what thrust is:

Thrust is a force produced by an engine that speeds up the motion of an object

Describe what upthrust is:

When an object is fully or partially submerged in a fluid, the fluid exerts an upward-acting push force on the object

Due to which force does a boat float on a lake?

Upthrust exerted by the water on the boat

What does an electrostatic force act between?

An electrostatic force acts between two objects with charge

What does a magnetic force act between?

A magnetic force acts between objects with magnetic poles

When does tension occur?

Tension occurs in an object that is stretched

In what three ways could a force affect an object?

1. Changing speed

2. Changing direction

3. Changing shape

What is the normal contact force?

When an object rests on a surface, the surface exerts a push force on the object (acting at right angles to the surface)

What do vector quantities have?

Both a magnitude and a direction

What is displacement?

Displacement is the length and direction of a straight line drawn from the start point to the end point

Name 6 vector quantities:

1. Acceleration

2. Displacement

3. Force

4. Momentum

5. Velocity

6. Weight

What is a resultant force/net force?

The combined action of all the forces, determinign direction the object will move as a result and magnitude of the net force experienced

What is friction defined as?

A force which opposes the motion of an object

Why might a resultant force be negative?

When the resultant force acts in the opposite direction to the object’s motion

What is weight defined as?

The force experienced by an object with mass when placed in a gravitational field

What is stopping distance?

The stopping distance of a car is the total distance travelled during the time it takes to stop in an emergency

What is the stopping distance formula?

Stopping distance = Thinking distance + Braking distance

What is thinking distance defined as?

Thinking distance is the distance travelled in the time it takes the driver to react to an emergency and prepare to stop

What are the main factors affecting thinking distance? [2]

1. The speed of the car

2. The reaction time of the driver

What is reaction time?

A measure of how much time passes between seeing something and reacting to it

What is reaction time increased by? [3]

1. Tiredness

2. Distractions

3. Intoxication (i.e. consumption of alcohol or drugs)

What is braking distance?

The distance travelled under the braking force in metres (m)

The greater the speed of the vehicle, the [ ] the stopping distance

Larger

What are 4 factors that affect a vehicle’s stopping distance?

1. Vehicle speed

2. Vehicle mass

3. Road and brake conditions

4. Driver reaction time

What is terminal velocity?

Terminal velocity is the constant maximum speed reached by a falling object when the resultant force is zero

Describe how an object might fall from a height for a long mark question:

1. At the start, the only force acting is [ ] [ ] (air resistance is zero)

2. There is a [ ] [ ] [ ] [ ], causing maximum downwards [ ]

3. As [ ] increases, [ ] [ ] increases upwards

4. This reduces the downward resultant force, so the object continues to speed up, but at a [ ] rate of acceleration

5. Eventually, upwards air resistance [ ] until it [ ] downwards weight

6. The [ ] [ ] becomes zero, so acceleration stops and the object travels at a [ ] [ ] called [ ] [ ]

7. As speed [ ], air resistance [ ] again until air resistance [ ] weight

8. The resultant force returns to zero, reaching a new, lower terminal velocity safe for [ ]

1. At the start, the only force acting is weight downwards (air resistance is zero)

2. There is a large downwards resultant force, causing maximum downwards acceleration

3. As velocity increases, air resistance increases upwards

4. This reduces the downward resultant force, so the object continues to speed up, but at a decreasing rate of acceleration

5. Eventually, upwards air resistance increases until it equals downwards weight

6. The resultant force becomes zero, so acceleration stops and the object travels at a constant speed called terminal velocity

7. As speed decreases, air resistance decreases again until air resistance equals weight

8. The resultant force returns to zero, reaching a new, lower terminal velocity safe for landing

What is the symbol for force?

F (CAPITAL)

What is the limit of proportionality?

The point beyond which Hooke’s Law is no longer true when stretching the material

In the spring and rubber band experiment, how is the extension calculated?

By subtracting the original length from each of the subsequent lengths

What does Hooke’s Law state?

The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality

What is elastic behaviour?

The ability of a material to recover its original shape after the forces causing the deformation have been removed

Deformation is a change in the original shape of an object. Deformation can be either…

Elastic or inelastic

What is elastic deformation?

When the object does return to its original shape after the deforming forces are removed

What is inelastic deformation?

When the object does not return to its original shape after the deforming forces are removed

Momentum is a property that…

All moving objects have

It is difficult to change the direction of an object with a [ ] [ ]

It is difficult to change the direction of an object with a large momentum

When will the momentum of an object change?

The momentum of an object will change if:

1. Its velocity changes

2. Its direction changes

3. Its mass changes

What are the units of momentum?

kg m/s

What does the principle of conservation of momentum state?

The total momentum before an interaction is equal to the total momentum after an interaction, if no external forces are acting on the objects

What does Newton’s third law of motion state?

Whenever two objects interact, the forces they exert on each other are equal in magnitude and opposite in direction

How can the force of an impact in a vehicle collision be decreased?

By increasing the contact time over which the collision occurs

What are the three main vehicle safety features?

Crumple zones, seat belts and airbags

Why do these vehicle safety features work?

They [ ] [ ] [ ] from the impact and [ ] [ ] [ ] [ ] [ ] the force takes place, [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] and the vehicle to come to rest. The [ ] [ ] [ ] [ ] [ ] and risk of injury on a passenger.

They absorb the energy from the impact and increase the time over which the force takes place, increasing the time taken for the change in momentum of the passenger and the vehicle to come to rest. The increased time reduces the force and risk of injury on a passenger.

What is the moment of a force?

The turning effect produed when a force is exerted on an object

The size of a moment defined by the equation…

M = F x s

What does the principle of moments state?

If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot

What is the centre of gravity?

The point through which the weight of an object acts