Grade 8 Science – Mechanical Systems Mock Unit Test

Ellie is using a simple machine in her science project. It is called "simple" because:

• it requires no effort to operate

• it performs multiple complex tasks

• it consists of one basic mechanism

• it's electronically controlled

Answer explanation

A simple machine is termed 'simple' because it consists of one basic mechanism, making it easier to understand and operate compared to more complex machines.

Why were simple machines invented?

• To create work for engineers

• To make tasks easier

• To increase force use

• To eliminate technology

Answer explanation

Simple machines were invented to make tasks easier by reducing the effort needed to perform work. They help in lifting, moving, and applying force more efficiently, which aligns with the correct answer.

Ella is using a seesaw at the park. The pivot point of the seesaw is called the:

• axis

• joint

• load arm

• fulcrum

Answer explanation

The pivot point of a lever is called the fulcrum. It is the point around which the lever rotates, allowing the lever to lift or move a load effectively.

Ava needs to lift a flat rock into a pickup truck. The simple machine that would best help her is a (a)  

• axle
• joint
• load arm
• fulcrum

Answer explanation

The load arm is a simple machine that acts as a lever, making it easier to lift heavy objects like a flat rock into a pickup truck by providing a mechanical advantage.

William is using an inclined plane to move a heavy box into a truck. A disadvantage of using the inclined plane is:

• less effort required

• increased travel distance

• more complex setup

• one-way movement only

Answer explanation

A disadvantage of an inclined plane is the increased travel distance required to move an object up the slope, making it less efficient in terms of distance covered compared to lifting it directly.

Arjun is trying to split a log using a wedge. Why might this method be less efficient?

• Wedges require less energy

• Wedges increase friction

• Greater force over longer distances

• Too sharp to be effective

Answer explanation

Wedges can increase friction between surfaces, making it harder to move objects. This added resistance can lead to less efficiency in applying force compared to other tools that minimize friction.

Ellie is organizing her garage and comes across several tools and machines. Which of these is not a complex machine?

• Blender

• Hammer

• Bicycle

• Lawn mower

Answer explanation

A hammer is a simple machine, consisting of a heavy 'head' attached to a long handle, used for driving nails or breaking objects. In contrast, a blender, bicycle, and lawn mower are all complex machines with multiple moving parts.

Sophia is riding her bicycle to school. What does a linkage do in her bicycle?

• Transfers energy

• Absorbs force

Answer explanation

In a bicycle, the linkage transfers energy from the rider's pedaling to the wheels, enabling movement. This is crucial for the bike's functionality, making 'transfers energy' the correct choice.

Priya is working on a bicycle and wants to increase the speed of rotation of the wheels. Which gears should she use?

• Reducing gears

• Driving gears

• Driven gears

• Multiplying gears

Answer explanation

Multiplying gears increase the speed of rotation by having a smaller driving gear turn a larger driven gear, resulting in a higher output speed. This is why 'Multiplying gears' is the correct choice.

Aiden is building a model car and wants it to go faster. To achieve this, the driving gear in his model must be:

• equal in size to the driven gear

• larger than the driven gear

• smaller than the driven gear

• made of rubber

Answer explanation

To increase the speed of a gear system, the driving gear must be larger than the driven gear. This allows the driving gear to turn more slowly while making the driven gear turn faster, thus increasing overall speed.