Forces up to level 6 Flashcards
Explain the difference between a scalar and a vector
Scalars have size (magnitude) only
Vectors have both magnitude and direction
What are the three main vectors that you need to know at GCSE level?
Force (pushes and pulls)
Velocity (speed with direction)
Displacment (distance with displacement)
Which of these quantities are scalar and which are vectors:
time
mass
velocity
speed
displacment
distance
force
acceleration
volume
pressure
area
time = scalar
mass = scalar
velocity = vector
speed = scalar
displacment = vector
distance = scalar
force = vector
acceleration = vector
volume = scalar
pressure = scalar
Explain how forces are represented on a diagram
Example: sketch a diagram of the weight force acting on a falling ball
Forces are represented as arrows. The arrow starts on the object that the force is acting on an points in the direction the force is acting.
The length of the arrow represents the size of the force.
Example:
Explain the difference between contact and non-contact forces and give examples of each one
A contact for is a force that requires the two bodies to be touching for the force to act.
Examples: friction, air resistance, normal reaction force
A non-contact force is a force where the two bodies do not need to be touching for the force to act.
Examples: Weight, magnetic force, electric force
What is the unit of force?
What is its symbol?
The Newton
N
Explain how to use a scale diagram to represent the magnitude of forces
the length of a force arrow represents the size of the force. Create a scale where 1 cm is equivalent to a set number of Newtons. All the forces on that diagram must follow the same scale.
How do pairs of forces act when they are:
a) acting along the same line
b) offset from each other
a) if forces are acting along the same line they will add to create a resultant force. if the forces act in the same direction their magnitudes are addes, while they are subtacted if the forces are acting in opposite directions
b) if the forces are not acting along the same line then the object will begin to spin around. if the forces are acting in the same direction the object will move and spin.
Explain how you would investigate how different types of lubricant affect the size of the force of friction when one object slides over another.
- set up the equipment as shown in the diagram
- pull the block at a constant speed and measure the force required to do this. This is equal to the friction force between the block and the surface
- Repeat this 3 times and take an average
- add a lubricant to the surface of the block and repeat the investigation. Again do this 3 times and take an average
- Find the difference between the force required with and without the lubricant to assess the size of its effect
- Repeat the experiment with a range of different lubricants
Label the forces that are acting on this object
What is the resultant force of these two objects?
50N Upwards
What is the resultant force on this object?
5N Down
What is the effect on a stationary object of:
a) a resultant force of zero
b) a resultant force greater than zero
a) The object will remain at rest
b) The object will accelerate in the direction of the force
What is the effect on a moving object of
a) a resultant force of zero
b) a resultant force in the direction of motion
c) a resultant force opposite to the direction of motion
a) The object will continue to move in a straight line at a constant speed
b) the object will accelerate in the direction of the force
c) the object will decelerate (slow down)
Explain how to find the centre of mass of a symmetrical piece of card
Draw lines down two of the lines of symmetry, the centre of mass will be where the lines cross.
Explain how to find the centre of mass of an object that is not symetrical
- Put a hole in the piece of card and hang it from that point
- Hang a plumb line (a piece of string with a weight on the end) from that point and draw a line down the card where the plumb line lays
- Make a second hole in the card in a different position and repeat steps 1 and 2
- The position where the lines cross is the centre of mass of the object
Define the centre of mass of an object
When an object is suspended (hanging downwards) how does the position of the centre of mass affect how it hangs?
The centre of mass of an object is the point at which all of the weight force appears to act
When an object is suspended it will hang so that the centre of mass hangs directly below the place that it is suspended from
Explain why a suspended object comes to rest with its centre of mass directly below the point of suspension (the point that it is hanging from)
When the centre of mass is to one side of the point of suspension, it will cause the objet to swing to the other side.
When it has swung to the other side, the centre of mass is now on the other side of the pivot so it swings back the way it came
when the centre of mass is directly below the pivot there is no turning force so the object does not swing at all
What makes an object that has been tipped fall over insttead of falling back onto its base
What are the factors that make it easier or harder for something to be tipped over
An object will fall over if its centre of mass lies outside of the pivot (the corner that it is balancing on)
Something will be easier to tip over if it has a narrower base or has a higher centre of mass.
Explain what a resultant force is
A resultant force is the overall effect of two or more forces. This means that the two or more forces can be replaced by a single force that has the same effect.
Explain how you can find the resultant force of these two forces.
- Create a scale drawing of the forces where the length of each force represents the size of the force
- Draw the forces end to end
- The resultant force is found by drawing an arrow from the start of the first force to the end of the second force
What does the term ‘resolving a force’ mean?
Resolving a force means splitting one force into two forces. These two forces when acting together have the same effect as the original force
Explain how you would reslove this force into its components
- Draw a scale diagram of the force at the correct angle
- Turn the force into a right angled triangle with the original force as the hypotenuse
- Measure the size of the sides of the triangle, these are the sizes of the horizontal and vertical components of a force
Explain how you can tell if there is a resultant force of zero when there is more than two forces acting
Draw a scale diagram of the forces with the start of each force starting at the end of the last one.
Each of the forces must be at the correct angle
If the forces make a complete loop then there is a resultant force of zero
