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GCSE physics > Forces and motion up to level 6 > Flashcards

Forces and motion up to level 6 Flashcards

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1
Q

Describe what a force is

Explain what forces do

A

A force is a push or a pull exerted by one object on another

Forces can change the speed that something is travelling (speed up or slow down), change the direction of something or change its shape

Forces are NOT needed to make something move at a constant speed.

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2
Q

Explain why a moving object does not need a resultant force to keep it moving

A

Resultant forces cause acceleration. If there is no resultant force it will not speed up or slow down, so it will continue to move in a straight line at a constant speed

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3
Q

State Newtons first law

A

If there is no resultant force on an object, if that object is at rest it will remain at rest. If the object is moving it will continue to move in a straight line at a constant speed.

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4
Q

State Newton’s second law

Example: what is the force required to make a 3kg mass accelerate at a rate of 8m/s2

A

Newtons second law states that the force needed to accelerate an object depends on the mass of the object ans how quickly it is being accelerated

Force = mass x acceleration

Force is measured in Newtons (N)

mass is measured in kilograms (kg)

acceleration is measured in meters per second squared (m/s2)

Example:

Force = mass x acceleration

= 3 x 8

= 24 N

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5
Q

Explain how to use an air track to investigate the the effect that increasing the force has on the mass of an object.

A
  1. Measure the total mass of the masses and the air track trolley combined
  2. Set up the air track with two light gates as shown in the diagram
  3. move one of the masses from the trolley to the string and calculate the weight force
  4. Let the trolley go and measure the acceleration of the trolley as it passes through the light gate
  5. Move a second mass from the trolley to the string and repeat the process. Repeat until all of the masses have been moved
  6. plot a graph of acceleration (y axis) against force (x axis)
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6
Q

What is the difference between mass and weight?

A

Mass is the amount of matter in an object and is measured in kilograms (kg)

Weight is the force that the planet exerts on an object due to gravity. It is measured in Newtons (N)

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7
Q

What are the two main forces that are acting when something falls?

A

The weight force is pulling downwards and air resistance is pushing upwards

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8
Q

Explain how to investigate the forces that are acting on an object that is falling through a fluid

A
  1. fill a glass measuring cylinder with a viscous fluid
  2. make marks on the measuring cylinder evey 5 cm
  3. Drop the object through the fluid and measure the time taken to pass between each set of marks
  4. when the time has become constant it means that the object has reached termial velocity where the weight and fluid resistance forces are balanaced
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9
Q

What happens to the acceleration of an object if

a) the mass is increased
b) the force is increased

A

If the mass is increased then it is harder to accelerate the object, this means that the acceleration goes down

If the force is increased then the object is getting a larger push, this means that the acceleration will increase

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10
Q

Explain how to calculate the weight of an object if you know the mass.

Example: what is the weight of a bag of flour with a mass of 1.5kg?

A

Weight can be found from this formula:

Weight = mass x gravitational field strength

Weight is measure in newtons (N)

mass is measured in kilograms (kg)

Gravitational field strength is measured in Newtons per kilogram (N/kg)

The gravitationa field strength on earth is always 10.

Example:

W = mg

= 10 x 1.5

= 15N

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11
Q

Explain why a falling object reaches a terminal velocity

A

As an object falls the weight force causes it to accelerate. As it accelerates it speeds up

The size of the air resistance force depends on the speed that the object is travelling, the faster the speed the larger the force.

This means that as the object speeds up the air resistance force increases, this reduces the resultant force and therefore the acceleration. Once it reaches terminal velocity the air resistance force is now equal to the weight force. The object will now fall at a constant speed as there is no resultant force

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12
Q

How can you investigate the relationship between mass and terminal velocity

A
  1. fill a class measuring cylnder with a viscous liquid
  2. make marks every 5 cm on the measuring cylinder
  3. drop a mass into the cylinder and time how long it takes to get between each mark
  4. Calculate the speed that the mass was travelling between each mark
  5. when there is no change between the speeds, terminal velcocity has been reached
  6. repeat the experiment for a range of masses (keeping the volume the same) and plot a graph of teminal velocity (y axis) agains mass (x axis)

The experiment could also be used to investigate the relationship between the mass of the object and how far it has to fall before reaching terminal velocity

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13
Q

Explain what the stopping distance of a car is

how is it sub divided?

A

The stopping distance of a car is the distance a car travels in the time from the hazard being percieved to the car stopping.

it is sub divided into:

thinking distance - the distance travelled in the time it takes to react to a hazard and start to apply the brakes

Stopping distance - the distance travelled in the time it takes for the car to stop once the brakes have been applied

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14
Q

Which factors can affect increase the thinking distance of a car?

A

Drugs and alcohol

Distractions

Useing mobile phones

Tiredness

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15
Q

Which factors can affect the braking distance of a car?

A

Heavily loaded car

Ice or water on the road

Poorly maintained tyres with not much tread

Work brakes that do not exert enough force

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16
Q

Explain how to calculate the thinking distance of a car.

A

Thinking distance can be calculated by the equation:

Distance = speed x time

The speed is the speed that the car is travelling and the time is the time it takes for the person to react after seeing the hazard

17
Q

Explain whether increasing the speed of a car has a greater effect on the thinking distance or the braking distance.

A

The an increase in the time taken to brake has a greater effect. this is because the thinking distance is directly proportional to the distance travelled due to the equation:

Distance = speed x time

This means that doubling the speed means the distance doubles

When braking, all of the kinetic energy needs to be removed from the car. as KE = 1/2 x mass x velocity2, if the speed doubles the energy (and therefore braking distance) increases by 4 (22) times

18
Q

What is momentum?

What is the equation for calculating the momentum of an object?

A

Momentum is the amount of motion that something has. Momentum can be increased by increasing the speed that the object is travelling with or the mass of the object

momentum can be found by:

Momentum = mass x velocity

Momentum is measured in kilogram meters per second (kgm/s)

mass is meausred in kilograms (kg)

velocity is measured in meters (m)

19
Q

What is the principle of conservation of momentum?

A

The total momentum before an event is equal to the total momentum after the event.

Remember that momentum is a vector, so something moving in the opposite direction to the original motion has a negative value.

You need to decide for yourself in each question which direction is positive and which one is negative

20
Q

Explain how to investigate the law of conservation of momentum when two trolleys explode away from each other

A
  1. Set up the equipment as shown in the diagram
  2. Measure the mass of each of the trolleys and record it
  3. Release the spring and time how long it takes for each one to hit the block on either side
  4. Measure the distance from the start to the blocks and use this to calculate the velocity of each block
  5. Find the momentum of each trolley using the equation:

momentum = mass x velocity

remember that one of the momentums will be positive and the other will be negative

  1. Add to gether the momentum of each trolley to show that the total momentum is zero. This proves the law of conservation of momentum.
21
Q

Explain what hooke’s law is.

Give the equation for Hooke’s law

A

Hooke’s law states that the extension of a spring is proportional to the force applied to it.

This means that the spring will stretch further if there is a gredater force upon it.

Hookes law is described by this equation:

Force = spring constant x extension of the spring

Force is measured in Newtons (N)

The spring constant is mearued in Newtons per meter (N/m)

Extension is measured in meters (m)

22
Q

Explain how to calculate the extension of a spring

A

The extenion of a spring is the the amount that it has streched by.

It can be calculated from this formula:

Extension = length of spring when stretched - length when not streched

23
Q

Explain how to investigate hookes law

A
  1. Set up the equipment as shown in the diagram
  2. measure the unstretched length of the spring and record this
  3. Add a 100g mass to the spring and measure the length of the spring. Make sure you measure it to the same part of the spring that you measured the first time around (e.g. the bottom coil)
  4. Calculate the extension and record this in the table
  5. Calculate the weight force and record this in the table
  6. Repeat the experiment, increasing the mass by 100g each time, for a range of masses from 100 to 600g.
  7. Plot a graph of Extension (y axis) against force (x axis)
24
Q

What is the limit of proportionality?

Explain how this limits the number of readings you can take when investigating Hooke’s law

A

The limit of proportionality is the extenion beyond which hookes law does not apply and the spring has a large strech for every extra mass added.

This limits the experiment becuase once this extension is reached the spring constant stops being constant. This means you cannot investigate massyes which take the spring beyond the limit of proportionality

25
Q

Explain how to calculate the force required to extend a spring form 10cm to 14cm if it has a spring constant of 5N/m

A

Use the equation:

Force = spring constant x extension

  1. First find the extension which is final length - original length

14-10 = 4cm = 0.04m

Remember to convert it into meters

  1. use the equation to find the force

F = ke

= 50 x 0.04 = 2N

26
Q

Which of these two objects follows hookes law? Explain how you know

A

Graph 2 obeys hookes law. This is becuase the extension is directly proportional to the force. This can be seen because the graph is a straight line that passes through the origin (0,0)

Graph 1 does not obey Hooke’s law. This can be seen becuase the line is curved.

GCSE physics (30 decks)

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